ScienceBits - A random walk in sciencehttp://www.sciencebits.com
The site and blog are written by a physicist, who, like the famous drunk, performs a random walk in science. Some of the static content is more serious, and hopefully, original.enReply to Eschenbachhttp://www.sciencebits.com/reply-eschenbach
<!-- google_ad_section_start -->Willis Eschenbach had a post on <a href="http://wattsupwiththat.com/2015/08/13/the-new-sunspot-data-and-satellite-sea-levels/">wattsupwiththat.com</a> attacking <a href="http://www.sciencebits.com/sunspots_2.0"> my post on this blog</a>, which explains why the new sunspot reconstruction may be irrelevant to the solar climate link and also discusses the recent paper I have co-written. I am not writing it as comments on whatupwiththat is for several reasons, but the main one is because Eschenbach's comments were condescending and pejorative. I am not going to degrade myself and have a discussion with him at his level on his web page. <br><br>
Now to the point. It is hard for me to find even one correct statement in Eschenbach's piece, which leaves so many wrong ones to address.
<br><br>
Let me start with his main crux. Eschenbach claims that in the paper by Howard, Svensmark and I, we have approximated the solar cycle as a sine with arbitrary phase instead of using a direct proxy. He then continues to fit the satellite altimetry data to the ENSO, and then fit the residual to the sunspot number. When he finds no correlation, he resorts to all sorts of negative remarks to describe our work, and in particular writes that "The journal, the peer reviewers, and the authors all share responsibility for this deception". <br><br>
To begin with, as Brandon Shollenberger commented in the comments section of that article, the use of harmonic analysis cannot be deception as we have specifically wrote in the paper what we are carrying out this analysis and why. A deception would be carrying out one analysis and writing that we did another. <br><br>
But more importantly, to reach his conclusions, Eschenbach assumes that if solar forcing has a large effect on climate, the sea level should vary in sync with it. This assumes that the sea level adjusts itself immediately to changes in the forcing. This ignores the simple physical fact that the heat capacity of the oceans is very large such that the oceans are kept far from equilibrium. Instead, it is the amount of heat, and therefore the sea level through thermal expansion that is expected to be proportional to the solar forcing. In other words, instead of comparing the sea level to the sunspot number, which is what Eschenbach did, he should have compared the sea level change <em>rate</em> to the sunspot number. If we look at his figure, and differentiate the sea level by eye, we see that this is exactly the case! <br><br>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/files/pictures/SSN2/Eschenbach-monthly-residual-sunspot-tsi.png" alt="No correlation because none expected!">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 1: Eschenbach's figure, where he correlates the altimetry data after it was detrended and had the ENSO component removed, with the sunspot number. He claims that there is no fit, but in fact, one expects the sea level <em>rate</em> to be largest when the sun is most active, and the sea level rate to be smallest when least active. This is seen in the data as expected!
</span>
</div>
</div><br>
It is quite upsetting that Eschenbach did this mistake even though it was clearly explained in our paper, and it is also explained in my <a href="http://www.sciencebits.com/calorimeter">previous paper from 2008</a>, where one can clearly see that the sea level change <em>rate</em> varies in sync with solar activity over more than 80 years. <br><br>
We also explain in the present paper why the altimetry data is important to pin point the exact phase, if there is a phase "mismatch" between the solar forcing and the sea level change rate. This is because any deviations from the "zero order" model in which sea level is just the integral of the absorbed heat (for which the sea level rate is in sync with the forcing) will teach us about additional processes, such as feedback of the climate system and the trapping of water on surface reservoirs. <br><br>
Studying this phase mismatch is simpler and clearer in a harmonic analysis, which is why we used it, but it is also possible to do it with a more direct solar proxy. I know this, because we also carried out the full analysis, but during the refereeing processes decided to leave it out as it didn't add any more physics while making the results more opaque. If anyone is bored, he or she can read this "supplementary material" describing this analysis <a href="http://phys.huji.ac.il/~shaviv/articles/Altimetry-AdditionalModel.pdf">here</a>.<br><br>
Eschenbach also complains that we have a seven parameter model and goes on to cite von Neumann's story about fitting Elephants. So first, because the fit is not empirical but physically based, one has to use all those relevant to describe the physics. For example, if we wish to describe the length of a rod as a function of temperature and force exerted on it, we will need the average length as well as both the thermal expansion coefficient and at least one elastic modulus. Can you describe this model with less than 3 parameters? Similarly, if you want to describe the solar forcing on sea level you need more than one parameter because solar forcing can primarily change the sea level through thermal expansion or though trapping of water on the surface. Since to first approximation the thermal expansion is the integral of the forcing and while the trapped water is the second integral of the forcing, at least 2 numbers are required to describe the effect of the solar forcing on sea level (two sines, or a sine with some phase), which is exactly what we have. Eschenbach writes that we used 3 numbers to fit the solar forcing, but the period wasn't a free parameter. It was set by observing the last solar cycle. A second trivial mistake is the claim that I have never heard of von Neumann's elephant quote. In fact, not only have I heard about it, I mentioned it in a <a href="http://www.sciencebits.com/FittingElephants">2007 blog post</a> that has elephants in its title! Trivially wrong and mixed with libelous claims. <br><br>
Next, in the beginning of his analysis, Eschenbach complains that "The 10Be beryllium [sic] isotope truly sucks as a solar proxy when used as it was in their study". This is wrong for several reasons. <br><br>
First, we didn't use it in "our study". I just mentioned Beryllium 10 as an example of a solar activity proxy showing that activity increased over the 20th century. <br><br>
Second, although the Beryllium 10 records have their problems, due to for example, a variable precipitation rate onto the ice sheets, if one compares them to Carbon 14 which are recorded in a completely different type of record, that of tree rings, one finds a generally good agreement between the two independent records, indicating that both reflect the same variability in cosmic ray spallation. For example, see <a href="http://www.nature.com/nature/journal/v493/n7434/fig_tab/493613a_F1.html">this figure</a>.<br><br>
Third, Beryllium 10 clearly show that solar activity increased over the 20th century. Anthony Watts himself <a href="http://wattsupwiththat.com/2012/09/13/paper-demonstrates-solar-activity-was-at-a-grand-maxima-in-the-late-20th-century/">wrote about it in his blog</a>, when he discussed Usoskin's paper studying this. <br><br>
Fourth, Eschenbach compares the Beryllium 10 to the sunspot number and finds a lousy correlation. He deduces from that, that Beryllium 10 "sucks as a solar proxy". However, this misses two important points that I made on my blog post: <br><br>
<ol>
<li> Solar activity can have various facets, and nobody promises us that long term variations in the solar wind will be the same as the long term variations in the sunspot number, so one is not necessarily lousier than the other, they just reflect different parts of the solar activity.</li>
<li> Moreover, if the Beryllium 10 record does not reflect what the sunspots do, then given the mounting evidence that cosmic rays are the direct link between solar activity (through modulation by the solar wind), the Beryllium record should be a much better indicator of the sun's affect on climate than sunspots. </li>
</ol><br>
Let me summarize Eschenbach's mistakes. Some are trivially wrong, some much worse. <br>
<ul>
<li>Eschenbach assumed in his analysis that if the sun has a strong solar forcing, the sea level should be in phase with it. This is plain wrong. Because of the high heat capacity of the ocean system, one roughly expects the sea level charge rate (and not the sea level itself) to be proportional to the solar forcing. If one looks at the slope of the sea level, it does indeed correlate nicely with solar activity. </li>
<li> Given that we explained how and why we carried out the fit using a harmonic analysis, we did not deceive anyone. Writing that we did is libelous. </li>
<li> The reason we used a harmonic analysis is because it makes the analysis more transparent. If one uses a solar forcing proxy (such as the cosmic ray flux), one finds a similar fit. Namely, writing that by using actual solar proxies one obtains a bad fit is simply wrong. (Again, one has to remember the heat capacity of the oceans!) </li>
<li> The model has 6 and not 7 parameters. Having all of them is necessary to compare the sea level to the physical model. To ridicule us that we used many parameters is totally irrelevant and inappropriate. </li>
<li> Eschenbach wrote that I haven't heard of von Neumann's Elephant quote. I did many years ago, and even mentioned it in a 2007 blog post on my blog. Trivially wrong, but reflects the low standards of that article. </li>
</ul> <br>
I should also add another point which is directed primarily to Anthony Watts. The Wattsupwiththat website used to keep very high standards. It also served as a very important outlet where discussions about various climate views, including those which do not conform to the dogmatic mainstream could be heard. However, the low standards borne from Eschenbach's article, both in science and in style should be avoided. Anthony Watts should not expose himself to libelous type of writing, which is exactly what Eschenbach has done. Writing false statements is one thing, it is Eschenbach's right for free speech, but writing that my colleagues and have "deceived" as well as other derogatory remarks that intend to tarnish our scientific integrity has no place in any scientific discussion. <br><br>
<!-- google_ad_section_end -->Sat, 15 Aug 2015 08:18:59 +0000shaviv279 at http://www.sciencebits.comhttp://www.sciencebits.com/reply-eschenbach#commentsThe Sunspots 2.0? Irrelevant. The Sun, still is.http://www.sciencebits.com/sunspots_2.0
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/18" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">cosmic rays</a>,&nbsp;<a href="/taxonomy/term/19" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">global warming</a>,&nbsp;<a href="/taxonomy/term/20" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">personal research</a>,&nbsp;<a href="/taxonomy/term/11" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">weather &amp; climate</a></div></div></div>After being asked by 5 independent people about the new sunspot number reconstruction and that it doesn’t show that the sun should have contributed any warming to the 20<sup>th</sup> century, I decided to write about it here. I have one word to describe it – irrelevant. It is also a good opportunity to write about new results (well, one that saw the light of day a few months ago) showing again that the sun has a large effect on climate. Yet, the world will still continue to ignore it. Am I surprised? No I’m not. <br><br>
First, what’s the story? A group led by Frédéric Clette had a presentation at the IAU assembly in Hawaii. In it, they argued that the sunspot number suffers from various systematic errors as it is a subjective measurement. Because those systematic errors vary with time (with the different observers and observational methods), the SN reconstruction can exhibit a fictitious long term trend. They also attempted to calibrate the data, and obtain a more homogeneous dataset. This is described at length in their <a href="http://arxiv.org/pdf/1407.3231v1.pdf">arXiv preprint</a>. <br><br>
The most interesting aspect about their new sunspot reconstruction is that there is significantly less variation in the sunspot number between the different solar maxima since the Maunder minimum. This implies, according to them, that there wasn't a significant increase in solar activity over the 20<sup>th</sup> century (no "20<sup>th</sup> century Grand Maximum"), and therefore the sun should not have contributed anything towards increased temperatures. This point was of course captured by the media (e.g., <a href="http://astronomynow.com/2015/08/08/corrected-sunspot-history-suggests-climate-change-not-due-to-natural-solar-trends/">here</a>). <br><br>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/files/pictures/SSN2/ssn2Fig1.jpg" alt="The old and new sunspot number reconstructions">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 1: The old (red) and new (blue) sunspot number reconstructions of Clette et al.
</span>
</div>
</div><br>
So, what do I think about it? First, I have no idea whether the calibration is correct. They do make a good argument that the SN reconstruction is problematic. Namely, some corrections are probably necessary and there is no reason a priori to think that what they did is invalid. However, their claim about solar activity in general not varying much since the sun came out from the Mounder minimum is wrong. There are other more objective ways to reconstruct solar activity than subjective sunspot counting, and they do show us that solar activity increased over the 20<sup>th</sup> century. So at most, one can claim that solar activity has various facets, and that the maximum sunspot number is not a good indicator of all of them. This is not unreasonable since the number of sunspots would more directly reflect the amount of closed magnetic field lines, but not the open ones blowing in the solar wind. <br><br>
The two important objective proxies for solar activity are cosmogenic isotopes (<sup>14</sup>C and <sup>10</sup>Be), and the geomagnetic AA index. The AA index (measured since the middle of the 19<sup>th</sup> century) clearly shows that the latter part of the 20<sup>th</sup> century was more active than the latter half of the 19th century. The longer <sup>10</sup>Be data set reveals that the latter half of the 20<sup>th</sup> century was more active than any preceding time since the Maunder minimum. (The <sup>14</sup>C is a bit problematic because human nuclear bombs from the 1940's onwards generated a lot of atmospheric <sup>14</sup>C so it cannot be used to reconstruct solar activity in the latter part of the 20<sup>th</sup> century). <br><br>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/files/pictures/SSN2/ssn2Fig2.gif" alt="The Geomagnetic AA index showing an increase in solar activity">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 2: The AA geomagnetic index showing a clear increase in solar activity over the 20<sup>th</sup> century (From <a href="http://www.ips.gov.au/Educational/3/1/4">here</a>).
</span>
</div>
</div><br>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/sites/default/files/pictures/climate/SolarActivityProxies.png" alt="The Beryllium 10 decrease from solar activity increase">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 3: The <sup>10</sup>Be production showing again, that the sun was particularly active in the latter half of the 20<sup>th</sup> century. The sunspot number is the "old" reconstructions without Clette's et al. corrections.
</span>
</div>
</div><br>
What does it tell us? Given that long term variations in Earth's climate do correlate with long term solar activity (e.g., see the first part of <a href="http://www.sciencebits.com/CosmicRaysClimate">this</a>) and given that some solar activity indicators (presumably?) don't show an increase from the Maunder minimum, but some do, it means that climate is sensitivite to those aspects of the solar activity that increased (e.g., solar wind), but not those more directly associated with the number of sunspots (e.g., UV or total solar irradiance). Thus, this result on the sunspots maxima (again, if true), only strengthens the idea that the solar climate link is through something related to the open magnetic field lines, such as the strength of the solar wind or the cosmic ray flux which it modulates. <br><br>
The second point I wanted to write about is a recently published analysis showing that the sun has a large effect on climate, and quantifying it. In an earlier work, I <a href="http://www.sciencebits.com/calorimeter">showed</a> that you can use the oceans as a calorimeter to see that the solar radiative forcing over the solar cycle is very large, by looking at various oceanic data sets (heat content, sea surface temperature and tide gauges). How large? About 6-7 times large than one can naively expect from changes in the solar irradiance. <br><br>
More recently, <a href="http://onlinelibrary.wiley.com/store/10.1002/2014JA020732/asset/jgra51778.pdf">Daniel Howard, Henrik Svesmark and I</a> looked at the satellite altimetry data. It is similar to the tide gauge records in that it measures how much heat goes into the ocean by measuring the sea level change (most of the sea level on short time scales is due to thermal expansion). Unsurprisingly, we found that the satellite altimetry showed the same solar-cycle synchronized sea level change as the tide gauge records. However, because the satellite data is of such high quality, it is has a higher temporal resolution than the tide gauge records which allows singling out the thermal expansion component from other terms (e.g., associated with trapping of water on land). This allows for an even better estimate of the solar forcing, which is 1.33±0.34 W/m<sup>2</sup> over the last solar cycle. You can see in fig. 4 how much the sun and el-Niño can explain a large fraction of the sea level change over yearly to decadal time scales. <br><br>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/files/pictures/SSN2/ssn2Fig4.jpg" alt="Altimetry based sea level data showing the solar influence">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 4: Sea level data and the model fit. The blue dots are the linearly detrended global sea level measured with satellite altimetry. The purple line is the model fit to the data which includes both a harmonic solar component and an ENSO contribution. The shaded regions denote
the one sigma and 1% to 99% confidence regions. The fit explains 71% of the observed variance in the filtered detrended data.
</span>
</div>
</div><br>
The bottom line is that the sun appears to have a large effect on the climate on various time scales. Whether or not the sunspots reflect the increase in solar activity since the Maunder minimum (as reflected in other datasets) is not very important. At most, if they don't reflect, it only strengthen's the idea that something associated with the solar wind does (such as the cosmic rays which they modulate). <br><br><!-- google_ad_section_end -->Mon, 10 Aug 2015 13:40:03 +0000shaviv278 at http://www.sciencebits.comhttp://www.sciencebits.com/sunspots_2.0#commentsHe who controls the past controls the future! On the vanishing global warming hiatushttp://www.sciencebits.com/he-who-controls-past-controls-future-vanishing-global-warming-hiatus
<!-- google_ad_section_start -->Two weeks ago a
<a href="http://www.sciencemag.org/content/early/2015/06/05/science.aaa5632.abstract">science paper</a> appeared claiming that once various systematic errors in the sea surface temperature are corrected for, the global warming “hiatus” is gone. Yep, vanished as if it was never there. According to the study, temperatures over the past 18 years or so have in fact continued rising as they did in the preceding decades. This meddling and adjustments of datasets was discussed elsewhere (e.g., on <a href="http://wattsupwiththat.com/category/hiatus-in-global-warming/">watts up with that</a>). Here’s my two pennies worth opinion of it. <br><br>
The first thing to note is that half a dozen other global surface temperature reconstructions do show a “hiatus”. Although it doesn’t invalidate the analysis (science is not a democracy!) it does raise an eyebrow, and should therefore be considered very cautiously.<br><br>
The second thing to note is that this result wasn’t obtained because they considered any new data, instead, they adjusted systematic corrections to different datasets and their respective weights. This is very dangerous. Even if it isn’t deliberate, there is a tendency for people to look (and force) corrections that might push results towards preferable directions, in this case to eliminate the “hiatus” and ignore corrections that could do the opposite. I am not saying this is the case, but I wouldn’t be surprised if it is. In any case, when adding inhomogeneous datasets (different buoys and ship intakes) that fact that different weights gives a different behavior (i.e., the existence or lack of a “hiatus”) is an indicator that the datasets are not added together properly! It is a sign that something is suspicious.<br><br>
<small>
<p align="center">
<a href="https://www.flickr.com/photos/claudiamarlene/15847818387" title="NOAA data buoy 46027 by Claudia Marlene, on Flickr"><img src="https://c2.staticflickr.com/8/7480/15847818387_bd527a478d_z.jpg" width="640" height="356" alt="NOAA data buoy 46027"></a>
</p>
A NOAA buoy swept ashore. Sea surface data was reconstructed with buoys as well as ship intakes. Since they measure water at different depths (and time varying average depth for the ship intake), systematic corrections have to be applied, but how large are they really?
</small><br><br>
Irrespective of the above (which should be regarded as caution signs), perhaps the most important discrepancy between the new surface temperature reconstruction and any dataset is with the satellite measurements. This is because the satellite measurements (which measure the atmospheric temperature and not directly the surface) have shown very little warming. So, if we are to accept the lack of any hiatus as real, we have to accept that the surface warmed much more than the atmosphere did. However, this is counter to any predictions of greenhouse warming. <br><br>
Greenhouse warming works by making the atmosphere more opaque to the infrared radiation. This implies that the effective layer from which radiation can escape back to infinity will reside higher in the atmosphere when more greenhouse gases are present, and since the atmosphere needs a typical temperature gradient to advect the energy from the surface to that emitting layer, the temperature all along the atmosphere has to increase. You can read more about it in <a href="http://onlinelibrary.wiley.com/doi/10.1002/joc.1651/epdf">Douglass et al. 2007</a> and see the figure below. Thus, increasing the surface temperature even more but removing the “hiatus” only aggravates the discrepancy! In other words, to really remove the “hiatus”, the NOAA people have to fiddle with the satellite data, not with sea surface data. <br><br>
<div class="eqcent">
<div class="thumb">
<div>
<img src="http://www.sciencebits.com/files/pictures/climate/warming-vs-altitude.jpg" alt="The atmosphere heating less than the surface. Eliminating the hiatus will only aggravate this discrepancy"></a>
<div class="thumbcaption" style="text-align: justify;">
<small>The warming vs. altitude, from <a href="http://onlinelibrary.wiley.com/doi/10.1002/joc.1651/epdf">Douglass et al. 2007</a>. One can readily see that the atmosphere heats less than the surface and less than climate models typically predict. Increasing the warming at the surface only aggravates the discrepancy. </small>
</div></div>
</div>
</div>
<br>
Last, hiatus or not, the whole discussion diverts everyone from the real problem that alarmists have. Even with the hiatus removed, the “larger” warming of about 0.1°C per decade is still much smaller than the range of predictions standard models make, implying that the models significantly overestimate climate sensitivity and therefore significantly overestimate future warming. For example, as you can see <a href="http://www.sciencebits.com/IPCC_nowarming">here</a>, a warming of 0.1°C/decade (i.e., 0.35°C over the 35 years of the graph) barely reaches the lower slope of the IPCC predictions.
<br><br>
In any case, the whole story reminded me of the hockey stick. One day we woke up in the morning and suddenly there was no medieval warm period and therefore no little ice age. The IPCC had a field day over it. It was the star of the third assessment report. We all know what happened afterwards with the climategate e-mails. I don’t know how this present story will unfold, but my suspicion is that the community and hopefully the public will be more cautious this time, but who knows. <br><br>
Let me end with a befitting quote:<br><br>
<blockquote>
“He who controls the past controls the future. He who controls the present controls the past.”<br>
― George Orwell, 1984
</blockquote>
Don't let them control your future or your past! <br><br><!-- google_ad_section_end -->Tue, 16 Jun 2015 14:30:14 +0000shaviv277 at http://www.sciencebits.comhttp://www.sciencebits.com/he-who-controls-past-controls-future-vanishing-global-warming-hiatus#commentsBill Nye, the not-so-good-science guyhttp://www.sciencebits.com/bill-nye-not-so-good-science-guy
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/15" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">general science</a>,&nbsp;<a href="/taxonomy/term/19" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">global warming</a>,&nbsp;<a href="/taxonomy/term/17" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">politics</a>,&nbsp;<a href="/taxonomy/term/11" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">weather &amp; climate</a></div></div></div><div class="myimage-right">
<img src="http://www.sciencebits.com/files/pictures/misc/BillNyeTheScienceGuy.jpg" />
<div class="myimage-caption">
Bill "the science guy" Nye says that I am a denier.
</div>
</div>
I recently stumbled on a transcript of Bill “the science guy” Nye’s interview on CNN last week. In it, he said that climate skeptics (i.e., people like myself), are at least as bad as people who deny that smoking causes cancer. There are quite a few things he misses, in fact, he got things totally wrong, but I do like the his analogy to smoking and cancer as you’ll see. <br><br>
First, what did he actually say? During his appearance on CNN, Bill Nye compared the link between denying a link between climate change and anthropogenic activity to denying a link between smoking and cancer: <br><br>
<div style="margin-left: 40px; font-style: italic; text-align: justify; font-family: times new roman,times,serif; ">
“I just want to remind voters that suppose you had somebody running for congressional office in your district who insisted there was no connection between cigarette smoking and cancer. Would you vote for that person? You might, but if this person were adamant — ‘No, the scientists who studied cigarette smoking, they don’t know what…’ — if they were adamant, would you vote for them? And so, in the same way the connection between climate change and human activity is at least as strong as cigarettes and cancer. And so, I just want everybody to keep this in mind: that it’s very reasonable that the floods in Texas, the strengthening storms, especially — the president was in Florida — these things are a result of human activity making things worse. It’s very bad. I get this that people died in Texas, and I am reminding you what else. This is a very expensive business. When you flood the fourth largest city in the United States, somebody is going to pay for it, and it’s you and me. And so, the sooner we get to work on climate change, the better.”
</div>
<br>
Here’s the actual video: <br>
<iframe width="560" height="315" src="https://www.youtube.com/embed/cnU3YEtTYw8" frameborder="0" allowfullscreen></iframe>
<br><br>
These short comments and comparison he made are inappropriate for several major reasons. <br><br>
To begin with, he follows the usual alarmist assertion that every calamity is necessarily due to global warming (now known as “climate change” so that they can cover more ground) and that all the climate change is necessarily anthropogenic. Since bizarre weather patterns can happen all the time with some probability, and since part of the climate change is also natural, these implicit “logical” steps would not make sense, at least in any other scientific discipline. I won’t dwell on this since others already did. <br><br>
Second, the global warming debate is mostly a quantitative one. While the IPCC claims that climate sensitivity can be very large (e.g., a 4.5°C increase per CO<sub>2</sub> doubling which would be catastrophic), I claim that such high values are ruled as they are inconsistent with a lot of empirical data (e.g., see this). In other words, skeptics like myself don’t argue that CO<sub>2</sub> has no effect on climate, only that the IPCC story is highly exaggerated. On the other hand, whether smoking contributes 90% or 10% of the cases of lung cancer would be good enough reason for any rational person to quit smoking (well, rational and able to overcome his or her addiction). On the other hand, if a given emission scenario over the 21<sup>st</sup> century will cause a 1°C or 4°C could make a huge difference. This means that denying that smoking causes cancer is a yes/no question while most skeptics don’t “deny anthropogenic global warming”, instead, they only claim it is minor. <br><br>
The third point is the main one I want to make. The reasoning behind the attribution of lung cancer to smoke and behind attributing global warming to anthropogenic activity is conceptually different, so different, that putting both on the same pedestal is simply wrong. The evidence linking lung cancer to smoking is in the form highly statistically significant increase in the incidence rate of lung cancer when comparing smoking to non-smoking groups. So, either smoking or something very closely related to it is clearly carcinogenic. The assertion that climate sensitivity is large, that most of the 20<sup>th</sup> century warming is necessarily anthropogenic and that temperature increase over the 21<sup>st</sup> century will be large are the result of model predictions, not on empirical evidence. In fact, empirical evidence such as the small response to volcanic eruptions (e.g., <a href="http://www-eaps.mit.edu/faculty/lindzen/184_Volcano.pdf">Lindzen and Giannitsis 1998</a>, see also note on <a href="http://www.sciencebits.com/FittingElephants">climate effects of volcanoes</a> here), or the lack of correlation between the order of magnitude CO<sub>2</sub> variations over geological time scales and the global temperature (e.g., this discussion on <a href="http://www.sciencebits.com/CosmicRaysClimate">cosmic rays and climate</a>), or of course, the lack of warming over the past nearly two decades, counter to all the model predictions (e.g., see this <a href="http://www.sciencebits.com/IPCC_nowarming">discussion of the hiatus</a> long before the term was used). <br><br>
If we use the cancer analogy it would be as if we had a model that can predict, at the biochemical level that some of the chemicals in cigarettes are carcinogenic, and that smoking should cause cancer, but, while the model would say that the incidence rate should be high and should explain most of the lung cancer cases, comparing the actual incidence rate would show that only some modest fraction of the lung cancer cases are attributed to smoking, but the rest are not. Yet, even with the evidence showing only a small difference in the incidence rate between the smoker and non-smoker group, the model will still be believed and it would be used to make predictions to other types of cancers, e.g., saying that they happen at a huge rate while they don’t. Sounds ridiculous? Well, this is what’s happening in climate science. <br><br>
Anyway, the last time I had any thought about the “science guy”, was when I heard he was to give the commencement speech at my wife’s graduation from Caltech (roughly when the global warming hiatus began!). Back then I thought of how uninspiring it is. I am not saying that publicizing science to the public is not important (which is what Bill Nye did so well), but I didn’t think that this is the kind of figure that will push the young cadet of scientists and engineers into new frontiers. Its isn’t as if he is doing rocket science. In retrospect, I now think it was even less appropriate to have him. <br><br><!-- google_ad_section_end -->Sat, 06 Jun 2015 05:29:29 +0000shaviv276 at http://www.sciencebits.comhttp://www.sciencebits.com/bill-nye-not-so-good-science-guy#commentsEuthanizing Overholt et al.: How bad can a bad paper be?http://www.sciencebits.com/Overholt_Melott_Pohl_is_really_wrong
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/10" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">astronomy</a>,&nbsp;<a href="/taxonomy/term/19" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">global warming</a>,&nbsp;<a href="/taxonomy/term/20" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">personal research</a>,&nbsp;<a href="/taxonomy/term/11" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">weather &amp; climate</a></div></div></div><div class="myimage-right">
<a href="http://en.wikipedia.org/wiki/Image:Foucaultspendulum.250px.jpg" alt="Milky Way Spiral Arms">
<img src="http://www.sciencebits.com/files/pictures/astronomy/MilkyWay.jpg" /> </a>
<div class="myimage-caption">
An artists conception of the Milky Way with its spiral arms
</div>
</div>
Last month I visited the U of Washington to give a talk in which I discussed the effects of cosmic rays on climate. At the end of it, not one, but two people independently asked me about <a href="http://iopscience.iop.org/1538-4357/705/2/L101">Overholt et al.</a>, which supposedly ruled out the idea that passages through the galactic spiral arms affect the appearance of glaciations on Earth (see < ahref="http://www.sciencebits.com/ice-ages">summary I wrote a few years ago</a>, which includes links to PDFs the actual papers). I told them that the paper had really stupid mistakes and it should be discarded in the waste bin of history, but given that Overholt et al. is still considered at all, I have no choice but to more openly euthanize it. <br> <br>
Before I get into the technical details (which will cause many of the readers to click their way out of here), I do want to say something general about the refereeing process and how it can easily break down, as it did here. <br><br>
Given that there are many more people who are eager to shoot down the cosmic ray climate link than people researching it, very often I find that the criteria used to accept papers which refute the link are way more lenient than the criteria needed to accept papers that supposedly refute it. This is because the refuters don't have an incentive to find errors in refuting papers (e.g., as I demonstrated with the <a href="http://www.sciencebits.com/Shakun_in_Nature">Shakun et al. paper supposedly finding that CO<sub>2</sub> leads the average global temperature</a>).
This is because any paper has a much higher probability of getting refereed by the refuter camp than the proponents camp. Simple statistics. <br><br>
The second comment is that I wrote them politely, it ended up with <a href="http://iopscience.iop.org/2041-8205/751/2/L45">an erratum</a>, but to save face they continued claiming the that their paper supports the erroneous claim that my original conclusions are unsubstantiated. One can show that even those leftover criticisms are plagued with errors. <br><br>
<h4>Main Problem</h4>
In the their paper, Overholt et al. try to estimate previous passages through the galactic spiral arms, and compare those passages to the appearance of ice-age epochs on Earth, over the past billion years. The gravest error is that the analysis was carried out using a spiral arm pattern speed that was totally different from the range of pattern speed they actually wrote they used! <br><br>
They wrote that they take 10.1 to 13.7 (km/s)/kpc as the possible range for the relative motion of the spiral arm pattern speed with respect to the solar angular velocity (i.e., a nominal value of about 11.9 (km/s)/kpc). However, if one looks at the average spiral arm crossing as obtained in their analysis, it is about 100 Myr (the first of their group of 4 arm passages is at roughly at 275 Myr and their second group is at roughly 670 Myr). This implies an average spiral arm passage every (670 Myr - 275 Myr)/4 ~ 100 Myr, which is inconsistent with the above pattern speed. In fact, an average spiral arm passage every 100 Myr implies a relative pattern speed of about:
$$ \Omega_\odot - \Omega_\mathrm{arm} \approx 15.4 (km/s)/kpc, $$
I am pretty sure that the source of error is the fact that they accidentally took the <em>absolute</em> pattern speed when calculating the spiral arm passages. For their nominal 217 km/s solar velocity at 8 kpc, one gets $\Omega_\odot = 27.1 (km/s)/kpc$, such that the absolute pattern speed obtained for the nominal 11.9 (km/sec)/kpc relative speed, is:
$$\Omega_\mathrm{arm} = \Omega_\odot - (\Omega_\odot-\Omega_\mathrm{arm}) = 27.1 − 11.9 = 15.2 (km/s)/kpc$$
i.e., roughly the value I read by eye from their graph describing the spiral arm passages. <br><br>
Because they accidentally took the absolute pattern speed, they obtained spiral arm crossings which are much more frequent that the climatic data or meteoritic data. If they would have taken the 10.1 to 13.7 range instead, the spiral arm passages would have been 112 to 152 Myr, which includes the ice-age epoch occurrences and the cosmic ray flux variations based on iron meteorites. The phase would have agreed as well. <br><br>
I then suggested that they publish an erratum to that paper, which they did. However, to save face, they claimed that their re-calculated spiral passages are still inconsistent with the meteoritic data or with the climate record, which brings me to the additional problems still present in their analysis. <br><br>
<h4> Additional Problems </h4>
A few more problems relate to the way Overholt et al. derive the spiral arm crossing (which is why even with their erratum, their manuscript is pointless). <br><br>
First, they take the spiral arm model of Englmaier et al. 2009, but they trace the spiral arms by eye, and as a consequence get a distorted result which gives highly unlikely “tight” clusters of 4 consecutive passages each rotation. In fact, it is so distorted that 2 consecutive arm crossings are of the same arm, which even with the radial epicyclic motion of the solar system is ridiculous. <br><br>
Second, they assume that their highly asymmetric (and unlikely) spiral arm configuration should remain as such for many spiral arm passages, but because the arms are dynamic, without more information, a more reasonable assumption would have been that the arms would have tended to be separated by 90 degrees instead of the “tight” clusters of 4 consecutive passages. <br><br>
Third, they didn’t consider the fact that supernovae are biased to take place about 10 to 20 million years after the spiral arm passage because of the finite lifetime of the stars that end their lives as supernova explosions. <br><br>
Fourth, they don’t actually carry out any statistical analysis how likely or unlikely is it to find all the ice-age epochs as close to the estimated spiral arm passages, not that a statistical analysis would have helped any given their problematic determination of the arm passages. <br><br>
Last, and perhaps most important. The cosmic ray flux can be shown <a href="http://www.sciencebits.com/JahnkeResponse">using Iron meteorites to be periodic with a roughly constant 145 Myr period</a>, and in phase with the appearance of ice-age epochs, which means that any distorted reconstruction such as that of Overholt et al. is inconsistent with the data, which they have totally ignored. <br><br>
<h4>Summary </h4>
Overhaul et al. analysis of the spiral arm passages is bad at so many levels it is not really worth ever considering again. However, will people still quote it and claim that it refutes the galactic spiral arm explanation for the appearance of spiral arm passages? Probably, but now you know better.<!-- google_ad_section_end -->Sun, 26 Apr 2015 05:31:15 +0000shaviv274 at http://www.sciencebits.comhttp://www.sciencebits.com/Overholt_Melott_Pohl_is_really_wrong#commentsBits of Science / Roundup #1http://www.sciencebits.com/bits-science-roundup-1
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/10" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">astronomy</a></div></div></div>Since I look for interesting science bits (mostly astro bits) for the Monday coffee of our astrophysics group, I realized that I could share it with the readers including some interpretation (and hopefully some added value) by your humble servant. So, here’s my try. If it works (and won’t be too much time) I’ll continue! Although for the coffee I bring mostly astrophysics and some planetary science, here I’ll also try to bring interesting results in climate (those that aren't lame...). <br><br><br>
<h3>Space and Planetary news bits</h3> <br>
<div class="myimage-right">
<img src="http://www.sciencebits.com/files/pictures/roundup/international-space-station-solar-eclipse.jpg" alt="International Space Station and Moon eclipsing the sun"/>
<div class="myimage-caption">
<span style="font-style: italic;">
The ISS and moon eclipsing the sun. Uncropped original at <a href=“http://www.astrophoto.fr”>www.astrophoto.fr</a> (with many more amazing photos on that site). </span>
</div>
</div>
• Solar eclipse by the moon and ISS <br><br>
You have all heard of (or seen?) the solar eclipse. What you may have missed is that that a few very lucky people actually experienced a double eclipse, partial by the moon and an “annular” eclipse by the international space station. See this image by <a href="http://www.astrophoto.fr">Thierry Legault</a>. <br><br>
A friend was surprised that the space station appears so large, but is it? <br><br>
The space station is at about 400 km (anything lower and its orbit will decay too fast, and anything higher will cost many more of the green stuff). If it has a span of about 100m, it will have an apparent angular size of about
$0.1~\mathrm{km}~/~400~{\mathrm km} \approx 1/4000~rad \approx 1’$ (about 1 arc minute, see <a href="https://www.google.com/search?q=1%2F4000+radians+in+arc+minute">google units</a>). Given that the diameter of the moon or sun is about 30’, the sizes in the image are reasonable. <br><br>
• Oceans on Ganymede <br><br>
<div class="myimage-right">
<img src="http://www.sciencebits.com/files/pictures/roundup/ganymede-aurora.jpg" alt="Aurorae on Ganymede"/>
<div class="myimage-caption">
<span style="font-style: italic;">
Aurorae on Ganymede (credit NASA/ESA).
</span>
</div>
</div>
It turns out that liquid oceans may be quite common to the solar system. Besides earth, Europa Enceladus and apparently also Ganymede have water oceans capped by a frozen surface. It is cold out there after all! However, the way that the oceans were “detected” on Ganymede (or more accurately “inferred”) is through the behavior of the auroral oval! <br><br>
The magnetic field around Ganymede has two components, one is its own generated (or probably relic) magnetic field, which is fixed to its rest frame. The second component is Jupiter’s magnetic field, however, unlike the first component, this one varies in a frame of reference fixed to Ganymede. Moreover, the location of the auroral ovals depend on the total field. However, because the total field varies, the aurorae are predicted to shift by 5.8° ± 1.3°. In reality, however, the measured variations had an extent of 2.2°±1.3°, <a href=“http://onlinelibrary.wiley.com/doi/10.1002/2014JA020778/abstract”>Saur et al.</a> used this to infer the existence of an ocean. How come? <br><br>
Well, a liquid ocean would be conductive (all it requires is just a small amount of salts), which would make the moon a big inductor if present. However, when you try to increase the magnetic field through an inductor, according to Lenz’s law, it will generate a magnetic field that will try to counteract the original magnetic field. The result is a smaller net magnetic field, and hence, the much smaller variation in the auroral oval! <br><br>
Interestingly, Lentz’s law also implies that the interaction between the induced currents and the generated field produce a force countering the motion. A neat example is this video: <br><br>
<iframe width="560" height="315" src="https://www.youtube.com/embed/liDjr439-fY" frameborder="0" allowfullscreen></iframe> <br><br>
It means that Ganymede has a VERY small “magnetic drag force” operating on it. <br><br>
<h3> Astrophysics news bits: </h3> <br>
<div class="myimage-right">
<img src="http://www.sciencebits.com/files/pictures/roundup/orion-explosion.jpg" alt="Gas blobs moving supersonically"/>
<div class="myimage-caption">
<span style="font-style: italic;">
Supersonic moving debris from an explosion that took place 500 years ago. The inset is the result of a simulation. How can the dense blobs be accelerated without being torn apart?
</span>
</div>
</div>
• Strange explosive event in Orion 500 years ago <br><br>
This is already about a month old, but I learned about it only last week, which is why I’m sharing. It appears that in the region of the Orion Nebula (on the “sword of Orion”), there is evidence for a very strange explosive event that took place about 500 years ago. The observations show dozens of what appears to be dense gas blobs moving super-sonically, withe their backwards trajectory emanating from a single point at a single instant. Their typical velocity is 300 km/sec (which is the typical escape speed from stars). This is very high velocity shrapnel! <br><br>
It really seems strange that it is possible to accelerate such dense gas blobs to such high velocities without disrupting them. But apparently it is possible. The image on the right shows the actual appearance of a few such blobs with the supersonic wake behind them. The inset picture is the result of a simulation, showing that typical Mach numbers of a 1000 are needed to reproduce the observations. You can read more about the observations and the simulations <a href="http://arxiv.org/abs/1502.04711">here</a>. <br><br>
• Supernova kaleidoscope <br><br>
<div class="myimage-right">
<img src="http://www.sciencebits.com/files/pictures/roundup/supernova-gravitational-lensing.jpg" alt="Gravitationally Lensed Supernova"/>
<div class="myimage-caption">
<span style="font-style: italic;">
Supersonic moving debris from an explosion that took place 500 years ago. The inset is the result of a simulation. How can the dense blobs be accelerated without being torn apart?
</span>
</div>
</div>
It is very common to find gravitationally lensed quasars and galaxies which have multiple images. What isn’t common is to find multiple images of a single supernova, as was recently <a href="http://www.sciencemag.org/content/347/6226/1123">discovered</a> for the first time . <br><br>
We can estimate the typical time delay between the images. Since the redshift of the lens is 0.54, it means that the typical distance to it is about half the age of the universe times the speed of light, or about $d = 5 \times 10^{9}$ light years. The perpendicular direction is of order the distance times the angle in radians. Since the separation between the lens and image it of order 1 arc-second, the real distance is about $r = 5 \times 10^{9} / 57/3600 \approx 25000$ light years (57 is the ratio between 1 radian and 1 deg, while 3600 is the ratio between one degree and one arc second). <br><br>
<div class="myimage-right">
<img src="http://www.sciencebits.com/files/pictures/roundup/galaxy-lensing.jpg" alt="Gravitational Lensing of a galaxy"/>
<div class="myimage-caption">
<span style="font-style: italic;">
Gravitational lensing implies that light can reach the observer through several paths traversed (source <a href="http://www.universetoday.com/116574/astronomers-discover-first-mulitiple-image-gravitationally-lensed-supernova/">universe today</a>). Each path may have a different duration, thus the images of the supernova should be delayed relative to each other.
</span>
</div>
</div>
The delay along the line of sight relative to the time it would take without the lensing galaxy is typically the extra distance the light has to traverse plus a gravitational time delay for having passed through the lenses’ gravitational well. However, we expect that both terms would be comparable (according to <a href="http://en.wikipedia.org/wiki/Fermat%27s_principle">Fermat’s principle</a>, light rays pass through extrema, which means that the two terms should be comparable). <br><br>
The time delay from the extra path is roughly
$$ \sqrt{d^2 + r^2} -d \approx { r^2 \over 2 d} \approx 0.06 \mathrm{~light~years~}\approx 3 \mathrm{~light~weeks}. $$
Thus, we expect the typical shifts to be a few weeks. Since SNe last longer than that, it is not surprising that one can see several images at the same time. <br><br><!-- google_ad_section_end -->Fri, 27 Mar 2015 04:27:51 +0000shaviv273 at http://www.sciencebits.comhttp://www.sciencebits.com/bits-science-roundup-1#commentsThe Funding Witch Hunthttp://www.sciencebits.com/funding-witch-hunt
<!-- google_ad_section_start --><div class="myimage-right">
<img src="http://www.sciencebits.com/files/pictures/misc/skeptic-witch-hunt.jpg" alt="skeptics witch hunt">
</div>
The recent <a href=“http://www.nytimes.com/2015/02/22/us/ties-to-corporate-cash-for-climate-change-researcher-Wei-Hock-Soon.html?_r=0”>bashing of Willie Soon</a> from the Harvard Smithsonian Center for Astrophysics in the NY Times exemplifies, I think, how the climate debate has long left the realm of science, and it also demonstrates how scientific research is most often funded, quite the opposite of what is generally portrayed! <br><br>
First, the reason I claim it isn’t a scientific debate anymore is quite obvious. The real debate should be on the observational or measured evidence and its theoretical interpretation, not on the funding responsible for the data collection or its analysis. The fact that the Willie Soon’s funding is questionable by some doesn’t imply that he is wrong. On the same token, opposite conclusions based on research funded by say Greenpeace cannot be automatically ruled out either. In the above NY Times bashing of Soon as well as in many other attacks on him, there wasn't any discussion on the key point he has tried to make, which is that the sun has a significant effect on climate yet it is mostly downplayed. In fact, I have been advocating this as well (e.g., you can quantify the <a href=“http://www.sciencebits.com/calorimeter”>solar radiative forcing</a> using the oceans, and find that it is 6-7 times larger than expected from just the solar irradiance variations). Since standard IPCC conclusions rely on 20th century modeling that only considers the small variations in the solar irradiance, those conclusions are mostly meaningless. <br><br>
The second point I want to emphasize is that the general public doesn’t realize that the funding of most scientists proceeds in an opposite way to that often perceived. Most scientists have a general plan or idea for the research they wish to carry out and then look for funding agencies or organizations that will fund that proposed research. It is not the opposite. Willie Soon, like many others, has an idea for the research he wishes to carry out, and looked for money to support his research framework, not the other way around! <br><br>
Similarly, Richard Muller of Berkeley had an idea he should independently reconstruct the 20th century warming. He looked for funding, and found it with the Koch Foundation that seeks to fund climate research that is not part of the mainstream (the latter of course doesn’t need additional support at it is amply funded by government agencies). Muller then proceeded to reconstruct the 20th century temperature (known as the BEST reconstruction) and study its implications. His were that most of the warming was anthropogenic and that the solar contribution was at most small. Did anyone hear complaints that his research is valid or invalid simply because it was the Koch foundation that funded him? Why then are people complaining when they funded Soon?
<br><br>
Of course, I do think there are <a href=“http://www.sciencebits.com/WorstBEST”>significant problems</a> with the conclusions that the BEST team reached, but they are all scientific. Similarly, if people do wish to criticize Soon, go ahead, but criticize his science not his funding. Attacking the funding is the feeble way of avoiding scientific debate. <br><br> <!-- google_ad_section_end -->Sun, 22 Mar 2015 04:26:01 +0000shaviv271 at http://www.sciencebits.comhttp://www.sciencebits.com/funding-witch-hunt#commentsSights from a Field Trip in the Milky Way: From Paleoclimatology to Dark Matterhttp://www.sciencebits.com/sights-field-trip-milky-way
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/10" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">astronomy</a>,&nbsp;<a href="/taxonomy/term/18" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">cosmic rays</a>,&nbsp;<a href="/taxonomy/term/20" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">personal research</a>,&nbsp;<a href="/taxonomy/term/11" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">weather &amp; climate</a></div></div></div>I was recently asked to write an article to “The Institute Letter” of Institute for Advanced Study at Princeton, where I am spending a wonderful sabbatical year. It briefly describes a very interesting discovery that my colleagues and I made, which is that the 32 million year oscillation of the solar system perpendicular to the galactic plane can clearly be seen in the paleoclimate data. In the article, I also discuss how the discovery came and some of its implications. I am bringing a slightly expanded version here (with more figures and elaborated caption), and references of course. Enjoy.
<br><br>The original article is found <a href="https://www.ias.edu/ias-letter/2015/shaviv-cosmic-rays">here</a>, and a pdf version <a href="http://www.sciencebits.com/files/pictures/32-Myr/winter2015_shaviv.pdf">here</a>.<br><br>
In 1913, Victor Hess measured the background level of atmospheric ionization while ascending with a balloon. By doing so, he discovered that Earth is continuously bathed in ionizing radiation. These cosmic rays primarily consist of protons and heavier nuclei with energies between their rest mass and a trillion times larger. In 1934, Walter Baade and Fritz Zwicky suggested that cosmic rays originate from supernovae, the explosive death of massive stars. However, only in 2013 was it directly proved, using &gamma;-ray observations with the FERMI satellite, that cosmic rays are indeed accelerated by supernova remnants. Thus, the amount of ionization in the lower atmosphere is almost entirely governed by supernova explosions that took place in the solar system’s galactic neighborhood in the past twenty million years or so. <br><br>
Besides being messengers from ancient explosions, cosmic rays are extremely interesting because they link together so many different phenomena. They tell us about the galactic geography, about the history of meteorites or of solar activity, they can potentially tell us about the existence of dark matter, and apparently they can even affect climate here on Earth. They can explain many of the past climate variations, which in turn can be used to study the Milky Way. <br><br>
The idea that cosmic rays may affect climate through modulation of the cosmic ray ionization in the atmosphere goes back to Edward Ney in 1959. It was known that solar wind modulates the flux of cosmic rays reaching Earth—a high solar activity deflects more of the cosmic rays reaching the inner solar system, and with it reduces the atmospheric ionization. Ney raised the idea that this ionization could have some climatic effect. This would immediately link solar activity with climate variations, and explain things like the little ice age during the Maunder minimum, when sunspots were a rare occurrence on the solar surface. <br><br>
In the 1990s, Henrik Svensmark from Copenhagen brought the first empirical evidence of this link in the form of a correlation between cloud cover and the cosmic ray flux variations over the solar cycle. This link was later supported with further evidence including climate correlations with cosmic ray flux variations that are independent of solar activity, as I describe below, and, more recently, with laboratory experiments showing how ions play a role in the nucleation of small aerosols and their growth to larger ones. <br><br>
In 2000, I was asked by a German colleague about possible effects that supernovae could have on life on Earth. After researching a bit, I stumbled on Svensmark’s results and realized that the solar system’s galactic environment should be changing on time scales of tens of millions of years. If cosmic rays affect the terrestrial climate, we should see a clear signature of the galactic spiral arm passages in the paleoclimatic data, through which we pass every 150 million years. This is because spiral arms are the regions where most supernovae take place in our galaxy. Little did I know, it would take me on a still ongoing field trip to the Milky Way.<br><br>
The main evidence linking the galactic environment and climate on Earth is the exposure ages of iron meteorites. Exposure ages of meteorites are the inferred duration between their breakup from their parent bodies and their penetration into Earth’s atmosphere. They are obtained by measuring the radioactive and stable isotopes accumulated through interaction with the cosmic rays perfusing the solar system. It turns out that if one looks at exposure ages a bit differently than previously done, by assuming that meteorites form at a statistically constant rate while the cosmic ray flux can vary, as opposed to the opposite, then the cosmic ray flux history can be reconstructed. It exhibits seven clear cycles, which coincide with the seven periods of ice-age epochs that took place over the past billion years. On longer time scales, it is possible to reconstruct the overall cosmic ray flux variations from a changed star formation rate in the Milky Way, though less reliably. The variable star formation rate can explain why ice-age epochs existed over the past billion years and between one and two billion years ago, but not in other eons. <br><br>
I later joined forces with Canadian geochemist Ján Veizer who had the best geochemical reconstruction of the temperature over the past half billion years, during which multicellular life left fossils for his group to dig and measure. His original goal was to fingerprint the role of CO2 over geological time scales, but no correlation with the paleotemperature was apparent. On the other hand, his temperature reconstruction fit the cosmic ray reconstruction like a glove. When we published these results, we instantly became personae non gratae in certain communities, not because we offered a data-supported explanation to the long-term climate variations, but because we dared say that CO2 can at most have a modest effect on the global temperature. <br><br>
Besides the spiral arm passages, our galactic motion should give rise to a faster cosmic ray flux modulation—in addition to the solar system’s orbit around the galaxy, with roughly a 250-million-year period, the solar system also oscillates perpendicular to the galactic plane. Since the cosmic ray density is higher at the plane, it should be colder every time the solar system crosses it, which depending on the exact amount of mass in the disk should be every 30 to 40 million years. <br><br>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/files/pictures/32-Myr/Galaxy-Motion.jpg" alt="The motion and trajectory of the solar system through the Milky Way (in spiral arms and perpendicular to the galactic plane)">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 1: The motion of the solar system through the galaxy. The main components (relevant to climate on Earth) are the periodic passages through the galactic spiral arms as it revolves around the galaxy, and the motion of the solar system perpendicular to the galactic plane (the horizontal “wavelength” of that motion is actually longer than portrayed in the cartoon).
</span>
</div>
</div>
A decade ago, the geochemical climate record showed hints of a 32-million-year periodicity, with peak cooling taking place a few million years ago, as expected from the last plane passage. Together with Veizer and a third colleague, Andreas Prokoph, we then submitted a first version for publication. However, we actually ended up putting the paper aside for almost a decade because of two nagging inconsistencies. <br><br>
First, analysis of the best database of the kinematics of nearby stars, that of the Hipparcos satellite, pointed to a low density at the galactic plane, which in turn implied a longer period for the plane crossings, around once every 40 million years. Second, it was widely accepted in the cosmic ray community that cosmic rays should be diffusing around the galactic disk in a halo that is much larger than the stellar disk itself. This would imply that the 300 light years that the solar system ventures away from the galactic plane could not explain the 1 to 2°C variations implied for the geochemical record. Without a way to reconcile these, there was not much we could do. Perhaps the 32 million years was just a random artifact. <br><br>
As time progressed, however, the improved geochemical record only showed that the 32-million-year signal became more prominent. In fact, fifteen cycles could now be clearly seen in the data. But something else also happened. My colleagues and I began to systematically study cosmic ray diffusion in the Milky Way while alleviating the standard assumption that everyone had until then assumed—that the sources are distributed symmetrically around the galaxy. To our surprise, it did much more than just explain the meteoritic measurements of a variable cosmic ray flux. It provided an explanation to the so-called Pamela anomaly, a cosmic ray positron excess that was argued by many to be the telltale signature of dark matter decay. It also explained the behavior of secondary cosmic rays produced along the way. But in order for the results to be consistent with the range of observations, the cosmic ray diffusion model had to include a smaller halo, one that more closely resembles the disk. In such a halo, the vertical oscillation of the solar system should have left an imprint in the geochemical record not unlike the one detected. <br><br>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/files/pictures/32-Myr/rawdata.jpg" alt="Raw geochemical oxygen 18 data proxying the paleoclimate over geological time scales">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 2: The raw &delta;<sup>18</sup>O data. Different colors correspond to different paleo-latitudes. The data exhibit a 140 or so million year oscillation and a much faster 32 million year oscillation.
</span>
</div>
</div>
Thus, armed with the smaller halo and a more prominent paleoclimate signal, we decided to clear the dust off the old paper. The first surprise came when studying the up-to-date data. It revealed that the 32-million-year signal also has a secondary frequency modulation, that is, it is periodically either slower or longer. This modulation has a period and phase corresponding to the radial oscillations that the solar system exhibits while revolving around the galaxy. When it is closer to the galactic center, the higher density at the galactic plane forces it to oscillate faster, while when far from the center, the density is lower and the oscillation period is longer. <br><br>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/files/pictures/32-Myr/Data-with-fit.jpg" alt="The temperature over geological time scales with the modeled temperature from the solar motion">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 3: The high pass filtered data, which has the 145 million year oscillation (due to spiral arm passages) removed. The data reveals a very distinct 32 million year oscillation which is naturally explained by the motion of the solar system perpendicular to the galactic plane.
</span>
</div>
</div>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/files/pictures/32-Myr/TvsZ.jpg" alt="The temperature as a function of height from the galactic plane">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 4: The &delta;<sup>18</sup>O data plotted against the modeled vertical location in the galaxy (normalized to the recent maximal excursion of the solar system around 20 Ma ago). The small orange dots are the actual 1 Ma binned data. The thick blue error bars are the averages of the combined data binned to 10 equal vertical bins. The red curve is a parabolic best fit. The additional points are a coarser binning of the latitudinally separated subsets. The fact that a similar vertical dependence appears in all 4 unrelated subsets indicates that the phenomenon is a global one.
</span>
</div>
</div>
<div class="myimage-plain">
<img src="http://www.sciencebits.com/files/pictures/32-Myr/rasterplot.jpg" alt="A raster plot showing the temperature as a function of time with a prominent 32 million year oscillation">
<div class="myimage-caption">
<span style="font-style: italic;">
Figure 5: The graph plots the temperature (red dots warm, blue dots cold) as a function of time (vertical axis) and as a function of time folded over a 32 million years period (horizontal axis and shown twice for clarity). The synchronization with the horizontal folding implies that Earth has had a clear 32 million year temperature oscillation. Overlaid on it is what appears to be a secondary "frequency" modulation, causing the apparent sine wave like behavior. The primary oscillation is consistent in both phase and period with the expected motion of the solar system perpendicular to the galactic plane. The secondary modulation is consistent in phase and period with the radial motion of the solar system (such that when it is closer to the galactic center, the density at the plane is higher, and the vertical oscillation is faster). The modeled peak warm and cold times are denoted with the open circles and connecting lines. Note that the temperature had the larger long term variations due to spiral arm passages are removed, allowing a clear view of the 32 million year oscillation.
</span>
</div>
</div>
The second surprise came when studying the stellar kinematics from the astrometric data. We found that the previous analysis, which appeared to have been inconsistent, relied on the assumption that the stars are more kinematically relaxed then they are. As a consequence, there was a large unaccounted systematic error—without it there was no real inconsistency. It took almost a decade, but things finally fell into place. <br><br>
The results have two particularly interesting implications. First, they bring yet another link between the galactic environment and the terrestrial climate. Although there is no direct evidence that cosmic rays are the actual link on the 32-million-year time scale, as far as we know, they are the only link that can explain these observations. This in turn strengthens the idea that cosmic ray variations through solar activity affect the climate. In this picture, solar activity increase is responsible for about half of the twentieth-century global warming through a reduction of the cosmic ray flux, leaving less to be explained by anthropogenic activity. Also, in this picture, climate sensitivity is on the low side (perhaps 1 to 1.5°C increase per CO2 doubling, compared with the 1.5 to 4.5°C range advocated by the IPCC), implying that the future is not as dire as often prophesied. <br><br>
The second interesting implication is the actual value of the 32-million-year oscillation. The relatively short period indicates that there is more mass in the galactic plane than accounted for in stars and interstellar gas, leaving the remainder as dark matter. However, this amount of dark matter is more than would be expected if it were distributed sparsely in a puffed-up halo as is generally expected. In other words, this excess mass requires at least some of the dark matter to condense into the disk. If correct, it will close a circle that started in the 1960s when Edward Hill and Jan Oort suggested, based on kinematic evidence, that there is more matter at the plane than observed. This inconsistency and indirect evidence for dark matter was also advocated by John Bahcall, who for many years was a Faculty member here at the IAS. <br><br>
It should be noted that the idea that cosmic rays affect the climate is by no means generally accepted. The link is contentious and it has attracted significant opponents over the years because of its ramifications to our understanding of recent and future climate change. For it to be finally accepted, one has to understand all the microphysics and chemistry associated with it. For this reason, we are now carrying out a lab experiment to pinpoint the mechanism responsible for linking atmospheric ions and cloud condensation nuclei. This should solidify a complete theory to explain the empirical evidence. <br><br>
As for the existence of more dark matter in the galactic plane than naively expected, we will not have to wait long for it to be corroborated (or refuted). The GAIA astrometric satellite mapping the kinematics of stars to unprecedented accuracy will allow for a much better measurement of the density at the plane. The first release of data is expected to be in 2016, just around the corner. <br><br>
More details can be found in the reference below (and much more information, in the supplementary material linked from that page). <br><br>
<h3>References</h3>
1. Is the Solar System's Galactic Motion Imprinted in the Phanerozoic Climate? Nir J. Shaviv, Andreas Prokoph & Ján Veizer Scientific Reports 4, Article number: 6150 doi:10.1038/srep06150, <a href="http://www.nature.com/srep/2014/140821/srep06150/full/srep06150.html">link</a>.<br><br><!-- google_ad_section_end -->Wed, 11 Mar 2015 13:29:58 +0000shaviv267 at http://www.sciencebits.comhttp://www.sciencebits.com/sights-field-trip-milky-way#commentsUpgraded site!http://www.sciencebits.com/site-upgrade-2015
<!-- google_ad_section_start -->About a year ago I decided to upgrade the site, but didn't get to finish it. The fact that the old site was eventually infected with a virus left me no choice but to finish the job! I hope you like it.
Also, given that I am now on sabbatical, it is not unlikely that you will even get to see fresh posts!<!-- google_ad_section_end -->Mon, 09 Mar 2015 15:55:35 +0000shaviv268 at http://www.sciencebits.comhttp://www.sciencebits.com/site-upgrade-2015#commentsA friend has passed awayhttp://www.sciencebits.com/calder
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/15" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">general science</a>,&nbsp;<a href="/taxonomy/term/19" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">global warming</a>,&nbsp;<a href="/taxonomy/term/11" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">weather &amp; climate</a></div></div></div>
In 1977 he made the movie &quot;the weather machine&quot; about how Earth is doomed to enter a new ice-age. Since those apocalyptic predictions did not materialize, he knew better once the wheels have turned and people talked about imminent warming. That is, his immune system developed immunity against blindly accepting alarmist predictions. <br><br>
When he learned of my friend Henrik Svensmark&#39;s work, he of course found it interesting, which is why several years later they ended up writing a book together, the Chilling Stars. <br><br>
As for myself, I met him just once. We had lunch in the restaurant opposite to the British Museum, but had plenty of e-mail correspondence. He will be fondly remembered. This is his last blog <a href="http://calderup.wordpress.com/2014/06/27/ive-gotta-be-driftin-along/">post</a>.</p>
<!-- google_ad_section_end -->Tue, 01 Jul 2014 18:36:12 +0000shaviv266 at http://www.sciencebits.comhttp://www.sciencebits.com/calder#commentsThe IPCC AR5 – First impressionshttp://www.sciencebits.com/AR5-FirstImpressions
<!-- google_ad_section_start --><div class="myimage-right"><img alt="IPCC AR5" src="http://www.sciencebits.com/files/pictures/climate/ipcc-ar5.jpeg" /></div>
<p style="text-align:justify">The IPCC summary for policy makers is out, and as I started writing these lines so was the last draft of the main report. Of course, it will take a while to digest the 2200 pages of the full report (it has a lot of starch!). Until I do, here are my first impressions from having read the summary and having skimmed the full scientific report.</p>
<p style="text-align:justify">My main conclusion is that this report is to a large extent a rehash of the AR4 report. However, given the lack of any new evidence pointing to humans and the increasing discrepancy between the alarmist models and predictions, the IPCC authors are bluntly making more ridiculous claims as they attempt to fill in the gap between their models and reality.</p>
<p style="text-align:justify">One of the statements which wonderfully exemplifies the absurdity of the new report is this paragraph discussing the climate sensitivity in the summary for policy makers. They write:</p>
<p style="text-align:justify"><cite>“The equilibrium climate sensitivity quantifies the response of the climate system to constant radiative forcing on multi-century time scales. It is defined as the change in global mean surface temperature at equilibrium that is caused by a doubling of the atmospheric CO<sub>2</sub> concentration. Equilibrium climate sensitivity is likely in the range 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence) 16. The lower temperature limit of the assessed likely range is thus less than the 2°C in the AR4, but the upper limit is the same. This assessment reflects improved understanding, the extended temperature record in the atmosphere and ocean, and new estimates of radiative forcing.”</cite></p>
<p style="text-align:justify">Now, have you noticed something strange? According to the AR4 report, the "likely equilibrium range of sensitivity" was 2.0 to 4.5°C per CO<sub>2</sub> doubling. According to the newer AR5 report, it is 1.5 to 4.5°C, i.e., the likely equilibrium sensitivity is now known <em>less accurately</em>. But they write: “This assessment reflects <em><strong>improved</strong> </em>understanding”. How ridiculous can you be?</p>
<p style="text-align:justify">More seriously, let me put this in perspective with the most boring graph I have ever plotted in my life. Below is the likely range of climate sensitivity as a function of time. As you can see, with the exception of AR4 with its slightly smaller range mentioned above, the likely range of climate sensitivity did not change since the <a href="http://www.atmos.ucla.edu/~brianpm/download/charney_report.pdf">Charney report</a> in 1979. In other words, after perhaps billions of dollars invested in climate research over more than three decades, our ability to answer the most important question in climate has not improved a single bit!</p>
<div class="myimage-plain"><img alt="IPCC AR5" src="http://www.sciencebits.com/sites/default/files/pictures/climate/SensitivityVsTime.jpg" style="height:369px; width:550px" /></div>
<p>One reason for the lack of improved understanding could be incompetence of the people in the field. That is, all the billions of dollars invested in climate research were not or could not be used to answer the most important question in climate, one which will allow predicting the 21<sup>st</sup> century climate change. I doubt however that this is the real reason. Among the thousands working in climate research, surely there are at least a few who are competent, if not more.</p>
<p>I think the real reason why there is no improvement in the understanding of climate sensitivity is the following. If you have a theory which is correct, then as progressively more data comes in, the agreement becomes better. Sure, occasionally some tweaks have to be made, but overall there is an improved agreement. However, if the basic premises of a theory are wrong, then there is no improved agreement as more data is collected. In fact, it is usually the opposite that takes place, the disagreement increases. In other words, the above behavior reflects the fact that the IPCC and alike are captives of a wrong conception.</p>
<p>This divergence between theory and data exactly describes the the situation over the past several years with the lack of temperature increase (e.g., as <a href="http://www.sciencebits.com/IPCC_nowarming">I described here</a> some time ago). It is also the reason why the IPCC had to lower the lower bound. The discrepancy is large enough now that a climate sensitivity of 2°C is inconsistent with the observations. However, under legitimate scientific behavior, the upper bound would have been decreased in parallel, but not in this case. This is because it would require abandoning the basic premise of a large sensitivity. Since the data requires a low climate sensitivity and since alarmism requires a large climate sensitivity, the "likely range" of climate sensitivity will remain large until the global warming scare will abate.</p>
<p>Incidentally, if one is not a captive of the high sensitivity idea, then things do converge, but they <a href="http://www.sciencebits.com/OnClimateSensitivity">converge towards a climate sensitivity</a> of about 1 to 1.5°C per CO<sub>2</sub> doubling.</p>
<p>A second important aspect of the present report is that the IPCC is still doing its best to avoid the evidence that the sun has a large effect on climate. They of course will never admit this <a href="http://www.sciencebits.com/calorimeter">quantifiable effect</a> because it would completely tear down the line of argumentation for a mostly manmade global warming of a very sensitive climate. More about it in a few days.</p>
<!-- google_ad_section_end -->Wed, 02 Oct 2013 19:11:01 +0000shaviv255 at http://www.sciencebits.comhttp://www.sciencebits.com/AR5-FirstImpressions#commentsGravity waves in rain clouds over the Arava valley http://www.sciencebits.com/GravityWavesInTheArava
<!-- google_ad_section_start --><div class="meta post-info">
<!--?php if ($submitted): ?--><p>Spring weather here in Israel was rather strange. Although winter with most of its precipitation should have been over, we had a few very rainy days. Now we're in the midst of a heat wave with temperatures as much as 20°C higher than just a week earlier.</p></div>
<div class="meta post-info">Anyway, on the last rainy day, there was some rain in the Arava valley (between the Dead Sea and the Red Sea). This area is a dessert and it normally gets very little rain (about 30mm/yr in the south and about twice at much in its north). But a serendipitous peak at the rain radar of the Israel Meteorological Service revealed a nice <strong>standing <a href="http://en.wikipedia.org/wiki/Gravity_wave">gravity wave</a></strong> over that area. A quick search with google didn't reveal any similar observation. That is, there are many travelling and standing gravity waves seen in clouds (either from the ground or from satellites), but none in a rain radar. Here are two consecutive snapshots of the radar, 10 minutes apart:</div>
<p style="text-align:center"><img alt="lee wave gravity waves seen in rain clouds" src="http://www.sciencebits.com/sites/default/files/pictures/weather/radarimage7n.gif" style="height:256px; width:256px" /><img alt="standing gravity waves generated by winds and seen in rain clouds" src="http://www.sciencebits.com/sites/default/files/pictures/weather/radarimage8.gif" style="height:256px; width:256px" /></p>
<p>Comparing them reveals that the rain pattern is exactly the same (i.e., it didn't propagate). This can be see the short animation:</p>
<p style="text-align:center"><img alt="" src="http://www.sciencebits.com/sites/default/files/pictures/weather/radarloop.gif" style="height:256px; width:256px" /></p>
<p>At first (before comparing consecutive snapshots!), I thought it was a traveling gravity wave (which I have seen quite a few times over Jerusalem, like the image at the bottom I took a day later), however, I then realized that it is a <strong>standing gravity wave</strong>. Namely, it is a wave formed by the sudden drop of air into the Arava valley. The wave which is excited is the one for which the phase speed is equal to the wind velocity. This is the wave which when traveling upstream will appear as standing and can therefore be amplified by the orographic feature. This is exemplified in this figure:</p>
<p style="text-align:center"><img alt="lee wave clouds" src="http://www.sciencebits.com/sites/default/files/pictures/weather/wave_clouds_schem.jpg" style="height:307px; width:500px" /></p>
<p>By comparing two radar snapshots, we can estimate the velocity of the rain cloud. It was 57 ± 12 km/hr. We can also measure that the distance between wave crests was 9.7±0.5 km. If the air would have been standing, this wave would have corresponded to an oscillation of 10 ± 2 min. This is actually consistent with my expectations.</p>
<p>The number to compare with is the <a href="http://en.wikipedia.org/wiki/Brunt-Vaisala_frequency">Brunt-Väisälä (BF) frequency</a> (or period). It is the oscillation that a parcel would have because of its buoyancy. Gravity waves have this oscillation for very large horizontal wave vectors but small vertical wave vectors. In the atmosphere, the BV oscillation period is typically 5 minutes or longer. It is longer for atmospheres which are more unstable and it becomes infinite when the atmospheres becomes convectively unstable (in convection, the BF is actually becomes imaginary).</p>
<p>Because the atmosphere wasn't very stable and because the wavelength is not very short (compared with the vertical scale height), we expect its oscillation period to be longer than the BV frequency, which itself is longer than the BV frequency of a very stable atmosphere. So, 10 mins is indeed reasonable.</p>
<p>A day after this radar image was taken, I saw another gravity wave. This time it was when waiting for my son's gym class to end:</p>
<p style="text-align:center"><img alt="gravity waves over jerusalem mountains" src="http://www.sciencebits.com/sites/default/files/pictures/weather/GravityWMaaletHaHamisha.JPG" style="height:318px; width:650px" /></p>
<p><strong>Travelling gravity waves </strong>are not uncommon in this mountainous area (or hilly, if 2500ft is a just "hilly" in your book). But other phenomena, such as <a href="http://www.sciencebits.com/KHoverJerusalem">Kelvin Helmholtz clouds</a> are...</p>
<!-- google_ad_section_end -->Sat, 27 Apr 2013 20:24:23 +0000shaviv253 at http://www.sciencebits.comhttp://www.sciencebits.com/GravityWavesInTheArava#commentsPredicting a supernova precursor (on SN2010mc)http://www.sciencebits.com/SN2010mc
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/10" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">astronomy</a>,&nbsp;<a href="/taxonomy/term/12" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">general physics</a>,&nbsp;<a href="/taxonomy/term/15" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">general science</a></div></div></div><p class="p1" style="text-align: justify;">A very interesting paper recently appeared in <a href="http://www.nature.com/nature/journal/v494/n7435/full/nature11877.html">nature</a>. It describes the detection of a <strong>precursor eruption</strong> of a supernova progenitor more than a month before the <strong>supernova explosion</strong> itself. It is particularly interesting because this detection was not serendipitous—it was based on my prediction.</p><p class="p1" style="text-align: justify;"><img alt="" src="http://www.sciencebits.com/sites/default/files/pictures/astronomy/PTF10telv2.png" style="width: 690px; height: 226px;"></p><p class="p1"><!--break--></p><p class="p1" style="text-align: justify;"><span style="text-align: right; font-size: 10px; line-height: 14.44444465637207px;">pictures arranged by&nbsp;</span> <a href="http://users.obs.carnegiescience.edu/mansi/" style="text-align: right; font-size: 10px; line-height: 14.44444465637207px;">Mansi Kasliwal</a></p><p class="p1" style="text-align: justify;"><u>Some background&nbsp;</u></p><p class="p1" style="text-align: justify;">In a supernova explosion, the envelope of a star (whether a massive star or a white dwarf) is blown away. Because it takes a long time for the thermal energy of the explosion to diffuse, instead of diffusing out and shining brightly, the thermal energy is all used to accelerate the shell. By the time the thermal radiation can actually be radiated, it is already gone and residing as kinetic energy. Without any other process, supernova would have been dim objects. But they are not.</p><p class="p1" style="text-align: justify;">Usually, the thermal energy used to illuminate supernovae comes from the radioactive decay of Nickel 56 and Cobalt 56 formed in the explosion itself. The radioactive decay heats the fast moving shell on a time scale of days to months, this energy then diffuses out and radiated away. That’s why the light curve of many supernovae can be described by a rise (due to the expanding shell being progressively more transparent) and then the exponential decrease associated with the radioactive decay of Nickel-56 (with a half life of 6 days) and Cobalt-56 (with a half life of 77 days).</p><p class="p1" style="text-align: justify;">However, in a subset of supernovae called <a href="http://en.wikipedia.org/wiki/Type_II_supernova">Type IIn</a>, some if not most of the thermal energy used to make the supernova shine originates from the supernova shell shocking circumstellar material, i.e., matter which was previously ejected by the progenitor star. Because the kinetic energy in the shell is much larger than the energy liberated in the radioactive decay of the Nickel and Cobalt, Type IIn supernova can therefore be very bright (depending on how much circumstellar matter there is to stop the shell).&nbsp;</p><p class="p1" style="text-align: justify;">This however raises the question, how did the circumstellar material get there to begin with? The typical amounts inferred from bright Type IIn lightcurves (and X-ray emission) can be several hundredths to several tens of solar mass. This cannot be explained by a “normal” wind of a massive star because those typically lose at least a hundred times less mass over the relevant time frame. This leaves two options.&nbsp;</p><p class="p1" style="text-align: justify;">The first one is that the circumstellar matter could have been the result of a pre-supernova <em>explosion</em>. Although this cannot be categorically ruled out, it doesn't seem to work in several cases. For example, you would tend to get a broader range of&nbsp;<span style="line-height: 1.5;">“</span><span style="line-height: 1.5;">narrow lines</span>”<span style="line-height: 1.5;">&nbsp;which have the typical </span><a href="http://en.wikipedia.org/wiki/P_Cygni" style="line-height: 1.5;">P-Cygni</a><span style="line-height: 1.5;"> spectral shape expected from a wind. This is because an explosion tends to produce a range of velocities while a wind had a much narrower distribution. In an explosion you would tend to see the SN&nbsp;envelope progressively shock faster moving material, but you generally don't.</span></p><p class="p1" style="text-align: justify;">The second option is that the matter was ejected as part of a dense wind accelerated during a super-Eddington phase.&nbsp; In short, the Eddington luminosity is the luminosity above which the radiative force outwards exceeds that of gravity. In principle, stars are not supposed to have steady states above this luminosity (which is proportional to the mass), because otherwise they would&nbsp;“evaporate”&nbsp;on short time scales. (To be more precise, they will have an extremely thick wind that will use all the available luminosity, keeping the luminosity well below the Eddington one). In practice, however, there are several types of objects which can exhibit <a href="http://www.sciencebits.com/SurpassingEddington">super-Eddington luminosities</a>. One example is the giant eruptions of <a href="http://en.wikipedia.org/wiki/Luminous_blue_variable_star">Luminous Blue Variables</a> (LBV). Another is classical nova eruptions. For example, the LBV star η-Carinae was about 5 times its Eddington luminosity for 20 years, while classical novae can reach as much as 20 times the Eddington luminosity for durations much longer than their dynamical time scales. Obviously, nature knows how to <a href="http://www.sciencebits.com/SurpassingEddington">bypass the Eddington limit</a>.&nbsp;</p><p class="p1" style="text-align: justify;">One of the interesting aspects of the super-Eddington state, however, is that it does accelerate a wind, one whose mass loss is predictable (see <a href="#Shaviv2002">Shaviv, 2002</a>). This mass loss is significant enough to explain the large amounts of circumstellar material found in the vicinity of the exploding supernova.&nbsp;</p><p class="p1" style="text-align: justify;">Another interesting piece of information suggesting that the circumstellar material is driven off in a super-Eddington eruption preceding the supernova is <a href="http://en.wikipedia.org/wiki/SN_2006jc">SN2006jc</a>. This is a very interesting type Ibn supernova (i.e., similar to a Type IIn supernova except that there was no hydrogen in the envelope) because Koichi Itagaki,&nbsp;a Japanese amateur astronomer, detected this object to have a super-Eddington LBV-like eruption a full 2 years before the SN&nbsp;explosion itself! Moreover, if one uses the mass loss luminosity relation I derived some 10 years ago (in <a href="#Shaviv2002">Shaviv 2002</a>), &nbsp;the mass that is predicted to have been ejected during the LBV-like episode is consistent with the&nbsp;circumstellar&nbsp;mass with which the SN shell appears to have interacted with (e.g., see modeling of <a href="#Chugai">Chugai&nbsp;2009</a>).</p><p class="p1" style="text-align: justify;"><u>The prediction</u></p><p class="p1" style="text-align: justify;">Given the LBV-like eruption seen in one Type Ibn supernova progenitor, and given that a super-Eddington episode can naturally explain the circumstellar material seen in many Type IIn (those with very dense circumstellar material), I realized that at least some Type IIn supernovae should be explain by pre-supernova super-Eddington outbursts.&nbsp;</p><p class="p1" style="text-align: justify;">So, back in May, <a href="http://www.weizmann.ac.il/home/eofek/">Eran Ofek</a> who is an observer at the Weizmann Institute visited the Hebrew University. While we were conversing in my office, I told him about this prediction, which got him interested. Since he is involved in the <a href="http://www.astro.caltech.edu/ptf/">Palomar Transient Factory</a> (PTF) project, he is in a position to look for such super-Eddington progenitors. This is because the PTF&nbsp;continuously monitors and records fixed regions in the sky. This means that when a supernova is detected at some direction, the same patch of the sky can be studied at <em>previous</em> epochs. In a sense, the PTF allows making a prediction backwards in time.&nbsp;</p><p class="p1" style="text-align: justify;"><u style="line-height: 1.5;">The discovery</u></p><p class="p1" style="text-align: justify;">On the same day he visited me, Eran checked and found that there are a few Type IIn supernova which could potentially have had detectable super-Eddington precursors. I then haven't heard from him until last&nbsp;<span style="line-height: 1.5;">September, at which point he e-mailed me and wrote that he indeed found a Type IIn supernova with a super-Eddington precursor. In fact, it was super-Eddington for 40 days preceding the supernova, reaching a peak luminosity of about 2500 times the solar Eddington luminosity (i.e., around 50 L<sub>Edd</sub> assuming a nominal 50 solar mass star).</span></p><p class="p1" style="text-align: justify;"><span style="line-height: 1.5;">The Light curve of this supernova with its unprecedented super-Eddington eruption is:</span></p><p class="p1" style="text-align: justify;"><img alt="" src="http://www.sciencebits.com/sites/default/files/pictures/astronomy/PTF10tel_lightcurve.png" style="outline-width: 0px; outline-style: initial; outline-color: initial; cursor: default; width: 610px; height: 439px; "></p><p class="p1" style="text-align: justify;"><span style="line-height: 1.5;">Together with the spectrum (see the&nbsp;<a href="#Ofek">paper</a>&nbsp;for the details), the following picture can be reconstructed:</span></p><p class="p1" style="text-align: justify;"><img alt="" src="http://www.sciencebits.com/sites/default/files/pictures/astronomy/PTF10tel_schematic.png" style="width: 690px; height: 215px; "></p><p class="p1" style="text-align: justify;">(pre-a) A super-Eddington eruption takes place over 40 days. During this time, it ejects a few 0.01&nbsp;M<sub>sun</sub> of material moving at 2000 km/sec. In addition, there is evidence of slowly moving material which was ejected at least several years before all the action takes place.</p><p class="p1" style="text-align: justify;">(a) By the time the supernova explodes, the ejected material reaches 7 <span style="font-size:9px;"><span style="font-family:arial,helvetica,sans-serif;">x</span></span> 10<sup>14</sup> cm.&nbsp;</p><p class="p1" style="text-align: justify;">(b) SN2010mc on day five. The fast moving supernova shock front (in grey) ionizes the inner and outer shells along the way, producing the broad and narrow hydrogen emission lines (from the 2000 km/s and 100 km/s outflows).</p><p class="p1" style="text-align: justify;">(c) The object at day 20, when the SN shock overruns the wind emitted in the super-Eddington phase. From this point, only the narrow hydrogen emission line is observed.&nbsp;</p><p class="p1" style="text-align: justify;"><span style="line-height: 1.5;">This discovery of course made me very happy. However, it didn't make me as happy as it would make me later!&nbsp;</span></p><p class="p1" style="text-align: justify;">The supernova light curve can be used in various ways to estimate the amount of matter present in the circumstellar material (CSM). These estimates constraint the amount present to be between 0.01 and 0.03 M<sub>sun</sub>.</p><p class="p1" style="text-align: justify;">The mass-loss - Luminosity relation I derived in 2002 can also be used to predict the amount of CSM that should have been ejected in the super-Eddington episode. It turns out to be around 0.05&nbsp;<span style="line-height: 1.5;">M</span><sub>sun</sub><span style="line-height: 1.5;">&nbsp;give or take a factor of 2. In other words, not only could I make a prediction which&nbsp;Eran Ofek discovered and confirmed, my 2002 results also consistently predict the amount of mass that should have been ejected during the super-Eddington episode, just before its spectacular death. Of course, it does open a very interesting question, which is why did the star become so luminous to begin with. To this I don't have a good answer. But that's what so beautiful in science, by answering one question you always open a few more interesting ones! In this case, the answers will probably&nbsp;</span><span style="line-height: 1.5;">have interesting ramifications to the very last stages of stellar evolution. &nbsp;</span></p><p style="text-align: justify;"><strong>References</strong>:</p><ul><li style="text-align: justify;"><a id="Chugai" name="Chugai"></a>N. N. Chugai,&nbsp;<span style="line-height: 1.5;">Circumstellar interaction in type Ibn supernovae and SN 2006jc, Mon. Not. Roy. Astro. Soc., 400, 866 (2009) [<a href="http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0908.0568">ads</a>]</span></li><li style="text-align: justify;"><a id="Kiewe" name="Kiewe"></a><span style="line-height: 1.5;">M.&nbsp;</span>Kiewe<span style="line-height: 1.5;">&nbsp;et al.,&nbsp;</span><span style="line-height: 1.5;">Caltech&nbsp;Core-Collapse Project (CCCP) observations of type&nbsp;IIn&nbsp;</span><span style="line-height: 1.5;">supernovae:&nbsp;</span><span style="line-height: 1.5;">typical properties and implications for their progenitor stars,&nbsp;</span><span style="line-height: 1.5;">The Astrophysical Journal, 744, issue 1, article id. 10, 19&nbsp;</span>pp<span style="line-height: 1.5;">&nbsp;(2012) [</span><a href="http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1010.2689" style="line-height: 1.5;">ads</a><span style="line-height: 1.5;">]</span></li><li style="text-align: justify;"><a id="Ofek" name="Ofek"></a>E. O. Ofek et al.&nbsp;An outburst from a massive star 40 days before a supernova explosion,&nbsp;Nature 494, 65–67 (07 February 2013) doi:10.1038/nature11877 [<a href="http://www.nature.com/nature/journal/v494/n7435/full/nature11877.html">nature</a>]</li><li style="text-align: justify;"><span style="line-height: 1.5;"><a id="Shaviv2002" name="Shaviv2002"></a>N. J.&nbsp;Shaviv,&nbsp;The theory of steady-state&nbsp;super-Eddington&nbsp;winds and its application to novae,&nbsp;Monthly Notices of the Royal Astronomical Society, 326, 126-146 (2002) [</span><a href="http://adsabs.harvard.edu/abs/2001MNRAS.326..126S" style="line-height: 1.5;">ads</a>]</li></ul><p style="text-align: justify;">&nbsp;</p><p>&nbsp;</p><!-- google_ad_section_end -->Fri, 15 Feb 2013 13:49:38 +0000shaviv252 at http://www.sciencebits.comhttp://www.sciencebits.com/SN2010mc#commentsVideo Lecture: Solar vs. Anthropogenic—Better Understanding of 20th Century Climate Changehttp://www.sciencebits.com/Munich-2012
<!-- google_ad_section_start --><p>Last month I participated in <a href="http://www.eike-klima-energie.eu/">EIKE's</a> (Europäisches Institut für Klima und Energie) conference on Climate Change. They video record the lectures, which means that mine is now online. I thought I'd share it with you. Have fun.</p>
<p><!--break--></p>
<p><iframe allowfullscreen="" frameborder="0" height="360" src="http://www.youtube.com/embed/8QtnueIJGjc?feature=player_detailpage" width="640"></iframe></p>
<!-- google_ad_section_end -->Tue, 15 Jan 2013 07:09:17 +0000shaviv251 at http://www.sciencebits.comhttp://www.sciencebits.com/Munich-2012#commentsDust Dendrites http://www.sciencebits.com/node/250
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/12" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">general physics</a>,&nbsp;<a href="/taxonomy/term/15" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">general science</a></div></div></div><p>My wife and I had our kitchen renovated. Since this involved breaking a few walls (and cutting out a new window), we knew it would raise a lot of dust. Mind you, here in the middle east houses are built from concrete and concrete blocks, not wood. To minimize the dust annoyance (and damage), we decided to quarter off the living room from the kitchen by using large nylon sheets hung from the ceiling to the floor. </p>
<p>After the dust settled down (literally…), we found something quite bizarre. The nylon walls developed very beautiful dust dendrites, akin to the more familiar frost dendrites (like these <a href="http://www.sciencebits.com/frostdendrites">frost dendrites</a> I have seen while living in Toronto). </p>
<p>I think the phenomenon occurs because the dust doesn’t stick easily to the nylon. So, as the air flows next to the nylon, dust can easily stick to already existing dust. This explains why a dust patch grows while areas around it don’t. However, in order to get dendrites there must be particular affinity to the dendritic tips. Namely, once a small protrusion is formed, it tends to grow on the expense of its neighboring regions. Clearly the dendrites have a small but important effects on the air flow next to it. Anyway, here are a few examples:</p>
<p style="text-align:center"><img alt="Dust Dendrites sticking to nylon, ghosts in dust" src="http://www.sciencebits.com/sites/default/files/pictures/Dendrites/Dendrites1.jpg" style="height:494px; width:700px" /></p>
<p style="text-align:center"><img alt="A ghost in the Dust Dendrites" src="http://www.sciencebits.com/sites/default/files/pictures/Dendrites/Dendrites2.jpg" style="height:452px; width:700px" /></p>
<p style="text-align:center"><img alt="Dust Dendrites on nylon" src="http://www.sciencebits.com/sites/default/files/pictures/Dendrites/Dendrites3.jpg" style="height:549px; width:700px" /></p>
<p>Later in the evening, when I was trying to clean up a little, I noticed a second interesting phenomenon. Some of the dust we have is paramagnetic. It stuck to the IKEA knife holder we have. In fact, it revealed the geometric structure of the magnets embedded in the holder.</p>
<p style="text-align:center"><img alt="Magnetic Dust sticking to magnet" src="http://www.sciencebits.com/sites/default/files/pictures/Dendrites/MagneticDust.jpg" style="height:465px; width:700px" /></p>
<p>At first I throughout it was quite strange that concrete dust would stick like that. However, when thinking about it more, concrete wasn’t the only thing cut. There was also some iron piping and the iron rods from reinforced concrete. Probably it is iron dust from them (making it ferromagnetic dust).</p>
<p>Well, this is the most fun I could have from the renovations. Otherwise it was a big annoyance… </p>
<!-- google_ad_section_end -->Wed, 02 Jan 2013 17:58:21 +0000shaviv250 at http://www.sciencebits.comhttp://www.sciencebits.com/node/250#commentsThe worst of the BEST http://www.sciencebits.com/WorstBEST
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/11" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">weather &amp; climate</a></div></div></div><p>I was asked by quite a few people about my opinion on the <a href="http://berkeleyearth.org/available-resources/">BEST analysis</a> of Richard Muller and his group in Berkeley. Since I didn’t want to keep my friends without an answer, I took a more careful look into the analysis. Here is what I think of it.<br>
<br>
There are two parts to the analysis. The first part is a reconstruction of the temperature over the 20th century. The second part includes analyzing this reconstruction and drawing various conclusions out of it.<br>
<br>
I will divide my discussion into the two parts. Since I am no expert in temperature reconstruction, and in particular on the possible biases that may appear, the first part will be rather short.<br>
<br>
<strong>The BEST temperature reconstruction</strong><br>
At face value, the methodology that Muller’s group takes seems novel and capable of reconstructing the data more systematically. Thus, I have no reason to doubt that this reconstruction could not in principle be superior to previous reconstructions.<br>
<br>
However, as pointed out by Ross McKitrick (<a href="http://www.rossmckitrick.com/temperature-data-quality.html">on his site</a>, and the <a href="http://www.rossmckitrick.com/uploads/4/8/0/8/4808045/referee_report.pdf">actual report</a>), it has a major drawback. Presently, there is no publicly available information about the data used or all the details describing the analysis pipeline. Without being able to independently carry out the BEST reconstruction, it is impossible to check it, and it should therefore be considered very cautiously. <br>
<img src="http://www.sciencebits.com/files/pictures/climate/McKitrickBias.jpg" style="width:600px" alt="Urban heat island bias"><br>
<br>
<strong>Analysis of the BEST temperature reconstruction</strong><br>
The second part, that of analyzing the reconstruction, is more problematic. To understand where the problems are, let us summarize the conclusions that Muller et al. reach from analyzing their data.<br>
<br>
- The BEST data indicates that there is little or no urban heat island effect.<br>
- There is no correlation with solar activity, indicating that it is not important for climate change.<br>
- They claim that the climate sensitivity to CO<sub>2</sub> changes are 3.1 ± 0.3°C per CO<sub>2</sub> doubling.<br>
- They claim that volcanos and CO<sub>2</sub> do a good job explaining the temperature increase over the 20th century.<br>
<br>
Let me address each one of these points.<br>
<br>
<strong>There is no urban heat island effect</strong><br>
In the Muller et al. analysis, "Very Rural" sites were defined as those locations which are 0.1° distant from an urban, i.e., from pixels defined as "urban" using the MODIS satellite. They then find that the average temperature minus the rural average temperature exhibits no trend (-0.10 ± 0.24°C/century over the past 50 years, or a net contribution of −0.05 ±0.12 °C at 95% confidence over this period).<br>
<br>
For comparison, the analyses of McKitrick &amp; Micheals (<a href="http://www.socratesparadox.com/Temperatures/McKitrick_Michaels2004.pdf">2004</a>, <a href="http://www.webcommentary.com/docs/rrm-pjm-1207.pdf">2007</a>) and McKitrick &amp; Nierenberg (<a href="http://www.rossmckitrick.com/uploads/4/8/0/8/4808045/final_jesm_dec2010.formatted.pdf">2010</a>) do show that there is a large effect. Here, the authors correlate the spatial distribution of warming with the spatial distribution of socio-economic index growth, and they find a significant correlation. To check their results, they correlate the rise in the socio-economic index with a GCM modeled temperature rise, and see no correlation. They conclude that the real temperature data therefore has contamination from urbanization.&nbsp;<br>
<br>
The truth is that when I originally read the different papers, I couldn’t say anything definitive myself (at least, not without spending more time I didn’t have). However, I did meet Ross McKitrick at the end of the summer, so I could actually ask him in person. The answer I got is very interesting (and you can find it in the <a href="http://www.rossmckitrick.com/uploads/4/8/0/8/4808045/referee_report.pdf">referee report</a> he wrote about BEST).<br>
<br>
According to McKitrick, one has to be very careful when considering the urban heat island effect because it is easy to get counter intuitive effects.<br>
<br>
Suppose we consider an effect (like the figure below) which grows logarithmically with time (because it is sensitive to the initial increase with population but less sensitive once the population is large). In such a case, the derivative of the temperature with respect of the population will be large when the population is small and small when the population is large. The bias will then be more pronounced when the population is small, not when it is large. However, because the BEST group didn’t characterized their very-rural sites, it is very hard to check whether such a bias exists or not. In other words, the fact that they don’t see an urban heat island effect doesn’t mean that it is not there.<br>
<br>
<strong>No correlation with solar activity. </strong><br>
The claim that there is no correlation between solar activity and the BEST temperature reconstruction, seemed strange to me when I first read it. The reason is that it is evident from a large body of work (including that which I have done) that the sun has a clear effect on climate and it is large. Perhaps the best single piece of evidence that not only unequivocally proves that the sun has an effect on the climate, but actually quantifies is in terms of radiative forcing, is the heat which goes into the oceans every solar cycle. This can be readily seen in the total oceanic heat content, in the sea surface temperature and most beautifully in the tide gauge records, as I elaborate in <a href="http://www.sciencebits.com/calorimeter">this post</a> .<br>
<br>
Given that Muller is a smart guy, and having met him, I know that he is an honest scientist (and an original one too), all I can say is that he is not aware of this data which unequivocally proves that the sun has a large effect on the climate.<br>
<br>
But this however doesn’t explain why the Berkeley group didn't see any correlation. So why didn't they?<br>
<br>
Muller et al. checked two correlations between their reconstructed temperature and the solar activity (which I presume is the latest irradiance reconstruction used by the IPCC, they don’t actually give a reference, at least I couldn't find it). One correlation is between the annual values of both records and the second correlation is between the decadally averaged values. Both lack of correlations are easy to understand, but they deserve separate considerations.<br>
<br>
The lack of correlation between the annual values is due to the fact that they are looking for an instantaneous linear relation, that is, they carry out a linear regression in the form $$T(t) =a F_\odot (t) + b \ln (pCO_2) + ... $$ However, the key point here is that Earth’s climate is a <a href="http://en.wikipedia.org/wiki/Low-pass_filter">low pass filter</a>. This means two things. First, the relation between the forcing and temperature changes and is not instantaneous (there is a lag and smearing because of the heat diffusion, primarily in the oceans). Second, the ratio between the forcing and the response on short time scales and the ratio between the forcing and the response on long time scales is different (because of the low pass filter behavior of the climate system, it damps response over short time scales). The ratio is a factor of around 3 to 4 between the 11 year response and the centennial response. As a consequence, the fit suppresses any solar contribution over long times scales because the short term variations due to the solar cycle will ruin the fit. So, any linear regression to the annual data is bound to fail.<br>
<br>
The second correlation is between the decadally average data sets. Here, the problem is different. Because this averaging wipes out all the details on short time scales, the time series left has relatively little information. Because solar activity mostly increased over the 20<sup>th</sup> century, just like other things, a fit to the decadally averaged data cannot effectively constrain the solar contribution. According to the BEST team, this contribution is 0.6 ± 1.7 °C per W/m<sup>2</sup>. Although it depends on the exact solar reconstruction, one typically finds that the average solar activity increase over the 20<sup>th</sup> century is comparable to the variations between solar minimum to solar maximum over the 11 yr cycle. Since those are 0.17 W/m<sup>2</sup> (in the irradiance), one finds that Muller et al. constrain the solar contribution over the 20<sup>th</sup> century to be 0.1 ± 0.3°C (at one σ). My best estimate for the solar contribution is 0.3 to 0.4 °C (see <a href="http://www.phys.huji.ac.il/~shaviv/articles/20thCentury.pdf">Ziskin &amp; Shaviv</a>), i.e, consistent with their "null" result, which actually includes the real result within their large error.<br>
<br>
In other words, the BEST analysis either fails because their regression model assumes an instantaneous response and the same response on different time scales, or, it provides a result which is meaningless given the large error it provides. In any case, they have NOT proven that the sun does NOT have a large effect on climate.<br>
<br>
<strong>CO<sub>2</sub> + volcanoes do a good job fitting the 20<sup>th</sup> century. </strong><br>
<br>
The next claim of the BEST team is that just CO<sub>2</sub> and volcanic forcing does a good job fitting their reconstructed temperature time series. Well, they don't do a good job for two reasons.<br>
<br>
First, when we <a href="http://www.phys.huji.ac.il/~shaviv/articles/20thCentury.pdf">consider</a> the possibility that the sun has an effect on the climate, but do so in a model which considered the diffusive (low pass) behavior of the climate system on short time scales, then we obtain a fit which is significantly better. The variance between the modeled and observed land data that we find (with more constraints, because we fit also the ocean data as well!) is a factor of 1.8 times smaller than Muller et al. In other words, the BEST team may be doing a good job, but they are far from really being <em>best</em>. We are better. In fact, we also do twice better than GCM fits to 20<sup>th</sup> century. Our secret is of course that we allow the sun to have a large effect on the climate. This large effect on the climate should be an undisputed fact given the <a href="http://www.phys.huji.ac.il/~shaviv/articles/CalorimeterFinal.pdf">large changes in the ocean heat content</a> over the solar cycle. But alarmists developed a blind spot to evidence contradicting their claims.<br>
<br>
Second, the BEST fit is unphysical. In it, they used two independent prefactors relating the CO<sub>2</sub> forcing and the volcanic forcing to the temperature response. However, there is a physical relation. (Since the radiative forcing of volcanoes and of CO<sub>2</sub> is supposed to be known, choosing different prefactors is equivalent to having a different climate sensitivity for the two different processes). <a href="http://eaps.mit.edu/faculty/lindzen/184_Volcano.pdf">Lindzen and Giannitsis</a> have shown that if you impose a high climate sensitivity (which you need if you want to explain the 20<sup>th</sup> century with just CO<sub>2</sub>), then the volcanic response on short time scales is too large (that is, Muller et al. assume that the volcanoes are doing less than they should). We also find that volcanoes would produce too large an effect if the climate sensitivity is too large. This is another reason why our model prefers a low climate sensitivity. (The first being that it likes a solar contribution to fit the short term variations).<br>
<br>
<strong>Climate sensitivity is large</strong><br>
Given the above, it is clear why the Berkeley group obtain a high climate sensitivity. If all they have is just CO<sub>2</sub>, then yeah, you need a high sensitivity which is about 3°C per CO<sub>2</sub> doubling in order to explain 20<sup>th</sup> century warming. However, they are missing other forcings. For example, the indirect aerosol effect can increase their sensitivity (because it cools, but nobody knows by how much), while if you take the sun into account, the models prefer smaller sensitivities. Moreover, if one takes a real model which includes the diffusive components (and thus produce the lags/low pass filter behavior) one finds an even better fit with a preferentially low sensitivity. Now I must say that they did point out in their paper that they only used CO<sub>2</sub> to proxy all the anthropogenic activity and therefore the sensitivity should be modified, however, I am quite sure that people will start quoting their number as the real climate sensitivity with the ridiculously small error that they obtained. You have been warned.<br>
<br>
To summarize, I think the BEST methodology towards reconstructing the temperature has its merits. However, the conclusions from their follow up analyses are unfounded. This is primarily because they used modeling which is too simple (and with it they killed the solar effect) and unphysical (response to volcanic forcing is much smaller than the response to CO<sub>2</sub> forcing).<br>
<br>
Don’t get me wrong. I do think it is good that independent analyses are done to reconstruct the temperature. The response in the climate community was luke warm at best, partially because an “outsider” group came an entered their own territory. This just proves that independent analyses are important.</p>
<!-- google_ad_section_end -->Thu, 06 Dec 2012 16:51:58 +0000shaviv246 at http://www.sciencebits.comhttp://www.sciencebits.com/WorstBEST#commentsThe eye of the Hurricane http://www.sciencebits.com/node/245
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/17" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">politics</a></div></div></div><p>After being busy with the submission of two research proposal and trying to stay afloat with the pretty heavy teaching load I have this semester, I decided I should take a short break and post something on my blog. I actually have quite a few things I have been wanting to write about, but it seems that the most relevant thing is the the mini-war which is raging not to far from here. So, I thought I'd stray from my usual and write about the middle east. </p>
<p>Anyway, living in Israel is like perpetually living in the eye of a Hurricane. Everything around is in a big turmoil, but Israel itself manages to keep life surprisingly peaceful. It means that if you learn not to listen to the news every hour, you have a pretty good life.</p>
<p>As things would have it, as I finished writing the lines of the previous paragraph I had to take a pause and run to the shelter after hearing the eerie sound of a raid siren! This made me think of a few things.</p>
<p>First, I don't know why it is so eerie, perhaps it is the idea that you're now a sitting duck or the fact that you actually hear it from several sources simultaneously, giving the sound a strange tone to it (plus, making it impossible to localize). </p>
<p>Second, It is the first time I heard this siren since the first gulf war, when I (and other Israelis) served as Scud missile targets. In any case, I think this is the first time since the early 70's that rockets were sent towards Jerusalem. It seems that Hamas tried to target the Knesset (at least so they say), though they missed it by about 10 km. Of course, I won't say to which direction, since it is not a good habit to do! (In The Yom Kippur war, for example, a stupid news reporter told all the radio listeners, including the Syrians, that a FROG-7 missile landed on Migdal HaEmek, the Syrians then corrected their aim and hit the Ramat-David airbase killing a pilot). </p>
<p>Third, this single incident (well, I hope it remains single) makes you realize what Israelis living next to Gaza have been feeling for the past 10 years, which brings me back to what I was writing about before the siren.</p>
<p>Although for the most part, most of Israel has been enjoying a rather peaceful existence, this is not the case for everyone in Israel. Residents of towns next to the Gaza strip have been living under a barrage of rockets for the past 11 years. During this time, about 5500 rockets where launched towards these towns (over 10000 if you count the mortar shells too). For comparison, London during WWII was on the receiving end of about 10000 V-1 and V-2 rockets.</p>
<p>So, it is not surprising that Gaza is finally on the receiving end. Although I am pessimistic about it, I do hope it will take the taste of war from the Hamas for a few years—that they will think twice before launching even a single rocket towards Israel, just like the 2006 campaign in Lebanon made that border quiet from Katyusha's ever since.</p>
<p>It is however always good to put things in perspective. Over 10 years, around 20 Israelis died from rockets. 3 During the present campaign. The number of Gazans who died over the past week is roughly 20, of whom quite a few were militants (e.g., setting up rockets). For comparison, the number of road casualties in Israel is roughly 390 a year (5.2 per 100,000 per year, compared with 12.3 in the USA! we have very few drunk drivers...). About 850 Egyptians died turing the over throw of their government. 2000 died in Yemen, and perhaps 30000 in Libya. The number of Syrian's killed by Syrian's in the present civil war has been about 40,000. So, even the little war is still part of the peaceful eye of the Hurricane. </p>
<p>Let me end with a link or two. Talking about hurricanes, if you want to know what some clerics think about Hurricane Sandy, check this link on <a href="http://www.memri.org/clip/en/0/0/0/0/0/0/3637.htm" rel="nofollow">memri.org</a>. And if that didn't make you raise an eyebrow, look at this <a href="http://www.memri.org/clip/en/0/0/0/0/0/0/3636.htm" rel="nofollow">this link</a> (That site is excellent. All it does is translate arab media into english, letting us westerners really know what Arabs really think). </p>
<p>I could make it a more scientific blog entry by calculating why it takes 1.5 min for a rocket to get from Gaza to Jerusalem, or something about the balistics of the .22 Baretta I shot today (yep I did, makes you wonder doesn't it?), but I'll go to sleep instead.</p>
<!-- google_ad_section_end -->Fri, 16 Nov 2012 22:45:25 +0000shaviv245 at http://www.sciencebits.comhttp://www.sciencebits.com/node/245#commentsDoes the global temperature lag CO2? More flaws in the Shakun et al. paper in Nature.http://www.sciencebits.com/Shakun_in_Nature
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/19" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">global warming</a>,&nbsp;<a href="/taxonomy/term/11" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">weather &amp; climate</a></div></div></div>Over the past two weeks, perhaps a dozen people asked me about the recently published paper of Shakun et al. in <a href="http://www.nature.com/nature/journal/v484/n7392/full/nature10915.html">Nature</a>. It allegedly demonstrates that the global temperature followed CO<sub>2</sub> around the warming associated with the last interglacial warming, between 20 to 10 thousand years ago. (Incidentally, if you don't have a subscription to nature, take a look <a href="http://wattsupwiththat.com/2012/04/04/a-new-paper-in-nature-suggests-co2-leads-temperature-but-has-some-serious-problems/">here</a>). One guy even sent the story as a news item on NPR. So, having no other choice, I decided to actually read the paper and find what is it all about. Should I abandon all that I advocated over the past decade? <br><br>
First some prologue. One of the annoying facts for alarmists is that ice cores with a sufficiently high resolution generally show that CO<sub>2</sub> variations lag temperature variations by typically several hundred years. Thus, the ice cores cannot be used to quantify how large is the effect that CO<sub>2</sub> has on the climate. In fact, there is no single time scale whatsoever over which CO<sub>2</sub> variations can be shown to be the origin of temperature variations (not that such an effect shouldn’t be present, but because of its size, no fingerprint was actually found yet, even if you hear otherwise!). This fact stands as a nasty thorn in the alarmist story. So, it is no surprise that when Nature recently published that (finally) there is an observation showing that the temperature (and in particular, the average <em>global</em> temperature) lags CO<sub>2</sub>, that the alarmist community had a field day over it. <br><br>
The abstract specifically writes (my emphasis):<br><br>
<blockquote>These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase <b>warming driven by increasing CO<sub>2</sub> concentrations</b> is an explanation for much of the temperature change at the end of the most recent ice age.
</blockquote><br>
So, is there a catch? <br><br>
It turns out that there are several problems with the Shakun et al. analysis. Some have already been pointed by other people (e.g., <a href="http://wattsupwiththat.com/2012/04/08/did-shakun-et-al-really-prove-that-co2-precede-late-glacial-warming-part-1/">this</a>, or <a href="http://wattsupwiththat.com/2012/04/06/a-reply-shakun-et-al-dr-munchausen-explains-science-by-proxy/">that</a>). I will concentrate on two new problems that particularly offended my intelligence. <br><br>
<b> First point: Lags, what do they mean? </b> <br><br>
I usually start “reading” an article by studying the figures, this way I am not distracted by the interpretation of the authors. And, one of the first things I noticed over this first glance was that indeed the global temperature appears to lag the CO<sub>2</sub> variations, however, if you look at each hemisphere separately, it appears that the northern hemisphere lags the CO<sub>2</sub> by 720±330 years, but the Southern hemisphere temperature <b>leads</b> the CO<sub>2</sub> variations by 620±660 years. The same figure also reveals that the global temperature lags the CO<sub>2</sub> by 460±340 years, which is the main find of the paper. Here are these graph (and the original caption). <br><br>
<small>
<p align="center">
<img width=455pt src="http://www.sciencebits.com/files/pictures/misc/ShakunNature.jpg" alt="CO2 leads and lags the temperature"/>
</p>
a. The global proxy temperature stack (blue) as deviations from the early Holocene (11.5–6.5 kyr ago) mean, an Antarctic ice-core composite temperature record42 (red), and atmospheric CO<sub>2</sub> concentration (refs 12, 13 [in the nature paper, n.s.]; yellow dots). The Holocene, Younger Dryas (YD), Bølling–Allerød (B–A), Oldest Dryas (OD) and Last Glacial Maximum (LGM) intervals are indicated. Error bars, 1σ (Methods); p.p.m.v., parts per million by volume. b, The phasing of CO<sub>2</sub> concentration and temperature for the global (grey), Northern Hemisphere (NH; blue) and Southern Hemisphere (SH; red) proxy stacks based on lag correlations from 20–10 kyr ago in 1,000 Monte Carlo simulations (Methods). The mean and 1σ of the histograms are given. CO<sub>2</sub> concentration leads the global temperature stack in 90% of the simulations and lags it in 6%.
</small><br><br>
But what do the lags mean? First, it is clear from causality arguments that CO<sub>2</sub> is probably affected by the temperature of the southern hemisphere. I write "probably" and not "definitely", because from a logical point of view, we cannot rule out that some other thing affects both the SH temperature and the CO<sub>2</sub> with a larger lag. Nevertheless, this relation is actually quite reasonable given that the ocean temperature affects the equilibrium between carbon present in the oceans and CO<sub>2</sub> in the air. Since there is way more water volume in the southern oceans than there is in the northern hemisphere, it is clear that the CO<sub>2</sub> should be more sensitive to variations in the southern hemisphere than to variations in the northern hemisphere. <br><br>
However, the fact that the northern hemisphere temperature lags the CO<sub>2</sub> does not imply that the NH is actually affected by the CO<sub>2</sub>. Compare the following: <br><br>
I. Southern Hemisphere T -> CO<sub>2</sub> -> NH Temperature <br><br>
with <br><br>
II.Southern Hemisphere T -> CO<sub>2</sub> with one lag, Southern Hemisphere T -> Northern Hemisphere T with a larger lag (say, through global ocean currents). <br><br>
How can you differentiate between the two options? You can't! This means that the above result means nothing in particular, except as mentioned before, that CO<sub>2</sub> is probably affected by temperature, in particular, that of the southern hemisphere.
In defense of the authors, I must say that when they have written in the abstract "<b>an</b> explanation" and not "<b>the</b> explanation" (see quote above), they were accurately portraying the indecisiveness of their results...
<br><br>
<b>Second point: Global temperature?</b><br><br>
Given the fact that the global temperature is composed of the SH and NH and that one precedes and the other lags the CO<sub>2</sub>, is there any meaning to averaging the two? Perhaps not if the physical behavior is different (at least for the particular temporal window studied in their paper). Even so, one would imagine that such an average for the global temperature should be half of the NH and half of the SH. This is because, at least last that I checked, exactly half of the Earth's surface area is in the Northern hemisphere and half is in the southern hemisphere (unlike comparison of the land area, or the temperature proxy data in the Shakun et al. paper). <br><br>
With this in mind, I started playing with the data. I was <em>utterly surprised</em> to learn that in order to recover their average "global" temperature, I needed to mix about 37% of their southern hemisphere temperature with 63% of their northern hemisphere temperature. In other words, their "global" temperature is highly distorted towards the Northern hemisphere! It is therefore no surprise that once they do find a northern hemisphere temperature lag, also their global temperature exhibits a similar lag, but it is not a global temperature by any means! <br><br>
My suspicion is that the authors have a different averaging weight to the two hemispheres because of the asymmetry in their data distribution, however, their global temperature is close to but not exactly the ratio in the number of datasets in each hemisphere, so I don't actually know what they did. <br><br>
Together with the faults pointed out by other people (most notably on <a href="http://www.wattsupwiththat.com">WUWT</a>), the Shakun et al. paper should not be considered as anything which proves that CO<sub>2</sub> has a large effect on climate. My prophesy, though, is that the Shakun et al. paper will become a major hallmark in the next IPCC scientific report. This is because the alarmist community needs it badly as evidence that CO<sub>2</sub> has a large effect of climate. They will also ignore all the major flaws which exist in it, because it will be convenient for them to do so. I hope I'm wrong, but I feel I'm right, and not only because one of the co-authors on the paper is also a <a href="http://www.ipcc.ch/pdf/press-releases/ipcc-wg1-ar5-authors.pdf">lead author</a> of the upcoming IPCC AR5 report.<br><br>
<b> How much of the warming since the last ice-age should be attributed to CO<sub>2</sub>?</b> <br><br>
Since this is a science blog after all, I thought it would be appropriate to end this post with more solid science in it. <br><br>
Overall, there was a 3.5°C degree increase taking place concurrently to a CO<sub>2</sub> increase from 180 to 280 ppm. If the warming is entirely due to CO<sub>2</sub>, then the climate sensitivity should be ΔT<sub>x2</sub> ~ 3.5°C/log<sub>2</sub>(280/180), or about 5.5°C per CO<sub>2</sub> doubling. But as I explained above, this conclusions is not supported at all by the above correlation. However, it does imply that if anyone is calculating a probability distribution function for the temperature sensitivity to CO2, then they should cut it at 5.5°C, because it simply cannot be any larger than that. <br><br>
On the other hand, my best estimate for the <a href="http://www.sciencebits.com/OnClimateSensitivity">climate sensitivity</a>, is that CO<sub>2</sub> doubling should cause a 1 to 1.5°C temperature increase, or about 0.65 to 1°C for a 180 to 280 increase in the CO<sub>2</sub>. In other words, at most a quarter of the observed 3.5°C should have been caused by the CO<sub>2</sub> feedback. The rest is something else. <br><br>
<!-- google_ad_section_end -->Sat, 21 Apr 2012 14:49:41 +0000shaviv242 at http://www.sciencebits.comhttp://www.sciencebits.com/Shakun_in_Nature#commentsOpen letter to Rep. Adam Schiff, regarding SOPA and PIPA bills. http://www.sciencebits.com/LetToSchiff
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/13" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">computers</a>,&nbsp;<a href="/taxonomy/term/17" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">politics</a></div></div></div>Dear Rep. Adam Schiff (representing California's 29th district). <br><br>
Although I presently live outside the US, I am a registered voter in the 29th district which you represent. I kindly ask that you will drop your support of SOPA. <br><br>
The continuing infringement of intellectual property in the internet is clearly a major problem which should be addressed. I know, I have personally witnessed copyright infringement (both mine and of friends). However, SOPA and PIPA are bills that may address internet piracy but they will do so at a very costly price, they will infringe the freedom of speech! <br><br>
In addition to having witnessed copyright infringement, I have also experienced an attempt to hush me up through a copyright infringement allegation. Clearly, if SOPA or PIPA would have been intact, my voice over the internet could have been more easily silenced. The SOPA or PIPA blacklisting of sites will be the beginning of a very slippery slope! <br><br>
Let me also point out another aspect, one which is more apparent from where I presently live in Israel. One of the methods through which autocratic regimes, such as those found around israel, control their population, is through control of the internet. Clearly, we think of these "big brother" measures as anti-democratic and infringement of civil rights which those populations should have. Surely, the US cannot by seen as hypocritical - on one hand opposing this kind of behavior by autocratic regimes, but on the other, adopting this behavior at home. <br><br>
Please, do fight internet piracy, but do not do so with SOPA or PIPA. It will cause more damage than good. It will hurt democracy, and if you do continue to support it, it will hurt you in the next elections as well (you won't get my vote!) <br><br>
Sincerely, <br>
Prof. Nir Shaviv <br><br>
<iframe src="http://player.vimeo.com/video/31100268?byline=0&amp;portrait=0" width="400" height="225" frameborder="0" webkitAllowFullScreen mozallowfullscreen allowFullScreen></iframe><!-- google_ad_section_end -->Thu, 19 Jan 2012 19:49:56 +0000shaviv238 at http://www.sciencebits.comhttp://www.sciencebits.com/LetToSchiff#commentsCauses of Climate Change - Poll Resultshttp://www.sciencebits.com/ClimateChangePollResults
<!-- google_ad_section_start --><div class="field field-name-taxonomy-vocabulary-4 field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Blog topic:&nbsp;</div><div class="field-items"><div "field-item"> <a href="/taxonomy/term/15" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">general science</a>,&nbsp;<a href="/taxonomy/term/19" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">global warming</a>,&nbsp;<a href="/taxonomy/term/17" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">politics</a>,&nbsp;<a href="/taxonomy/term/11" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">weather &amp; climate</a></div></div></div>Out of curiosity, I opened a few weeks ago a poll asking the visitors of this site, what do they think is the primary cause of global warming. 429 people answered the poll (thanks to all of you!). <br><br>
The results can be summarized as follows. <br><br>
First, the visitors of this site have the following background:<br>
<table>
<tr>
<th width="50%">Background</th>
<th width="50%">Fraction (Votes)</th>
</tr>
<tr>
<td>Layman</td>
<td> 54.9% (232) </td>
</tr>
<tr>
<td>General Scientist </td>
<td>41.1% (174)</td>
</tr>
<tr>
<td>Climate Scientist </td>
<td>4.0% (17)</td>
</tr>
</table><br>
i.e., The audience of this website is clearly scientifically oriented (almost half are scientists). And what does this educated audience think about global warming?<br>
<table>
<tr>
<th width="50%">Cause of 20th century warming</th>
<th width="50%">Fraction (Votes)</th>
</tr>
<tr>
<td>Mostly Anthropogenic</td>
<td> 5.2% (22) </td>
</tr>
<tr>
<td>Mostly Natural </td>
<td>81.8% (346)</td>
</tr>
<tr>
<td>Nobody knows </td>
<td>14.9% (63)</td>
</tr>
</table><br>
Clearly, the highly educated visitors of this site have proven that global warming is mostly natural. Moreover, one can clearly see that the ratio of "mostly anthropogenic" to "mostly natural" decreases as the relevant scientific background increases: 0.04 in the laymen and general scientists groups, and 0%(!) in the climate scientists group. <br><br>
Ok, so seriously, what have I demonstrated? It is no surprise that my site attracts doubters of the anthropogenic global warming story. After all, I have been labeled as a "skeptic" (which I proudly am, since any real scientist should never take anything for granted). For this reason, the poll results are biased. But on the same token, it is clear that when someone says that 99% of all the scientists think this or that, it is totally meaningless. The reason is that mainstream science, whether it is correct or not, tends to inflate those that think alike. It is easier for them to publish and it is easier for the to get research grants to pay their salary or their students salary. Clearly, the mainstream will always have a stronger visibility (e.g., in terms of number of publications, citations, or even the number of people), but it doesn't prove that the mainstream is correct (see also what I wrote about it <a href="http://www.sciencebits.com/Expert-credibility-in-climate">here</a>). <br><br>
And now, after having carried out this poll, let me end with what different poll results really mean (with no offese to pollsters!) <br>
<ul>
<li>87.547% of all statistical polls are meaningless. </li>
<li>66.666% of all statistical polls are carried out with a very small sample. </li>
<li>99% of all statistical polls are pure propaganda! </li>
</ul>
Anyway, the moral of this experiment is that you should never trust a poll if you don't know who made it. And even if you do trust that person, [ like you trust me ;-) ], polls can be biased!
<br>
<!-- google_ad_section_end -->Mon, 16 Jan 2012 16:42:44 +0000shaviv237 at http://www.sciencebits.comhttp://www.sciencebits.com/ClimateChangePollResults#comments